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Opinion ARABIAN, J. The Director of Corrections appeals a superior court judgment and order on habeas corpus vacating an earlier superior court judgment against David Joseph Carpenter, including a sentence of death. We reverse. I. The Background A. The Santa Cruz “Trailside Murder” Case In the Santa Cruz Superior Court, the People charged Carpenter with the following offenses committed in that county in the spring of 1981: (1) the murder of Ellen Marie Hansen under special circumstances of rape murder, lying in wait, and multiple minder; (2) the attempted rape of Hansen; (3) the attempted murder of Steven Russell Haertle with personal use of a firearm and infliction of great bodily injury; (4) the murder of Heather Scaggs under special circumstances of rape murder and multiple murder; and (5) the rape of Scaggs. Carpenter pleaded not guilty. Following a change of venue because of pretrial publicity, a jury trial was held in Los Angeles County. The jury found Carpenter guilty on all charges, with the murders in the first degree, and found each of the allegations true. After the penalty phase, it returned a verdict of death, and the superior court imposed that sentence. Carpenter’s automatic appeal to this court is pending. B. The Marin “Trailside Murder” Case In a separate action, the one underlying this appeal, the People charged Carpenter with the following offenses committed in Marin County in the fall of 1980: (1) the murder of Cynthia Toshiko Moreland with personal use of a firearm; (2) the murder of Richard Edward Stowers with personal use of a firearm; (3) the murder of Anne Evelyn Alderson under the special circumstance of rape minder and with personal use of a firearm; (4) the rape of Alderson with personal use of a firearm; (5) the murder of Diane Marie O’Connell under the special circumstance of rape murder and with personal use of a firearm; (6) the attempted rape of O’Connell with personal use of a firearm; (7) the murder of Shauna Catherine May under the special circumstance of rape murder and with personal use of a firearm; and (8) the rape of May with personal use of a firearm. The special circumstance of multiple murder was also charged. Carpenter pleaded not guilty. After the trial for the Santa Cruz crimes, and following a change of venue because of pretrial publicity, jury trial in this case commenced in San Diego Superior Court. Prior to trial, the court ruled on the admissibility of evidence of the Santa Cruz “Trailside Murders.” Both parties theorized that the same person committed both sets of crimes; the issue at trial was whether that person was Carpenter. For the guilt phase, the court permitted evidence of the facts underlying these offenses except those against Scaggs; it excluded the latter as, inter alia, substantially more prejudicial than probative under Evidence Code section 352. For the penalty phase, it permitted evidence of the facts underlying all the offenses. For both phases, it barred evidence of Carpenter’s convictions and death sentences as substantially more prejudicial than probative. Throughout jury selection and trial, the court continually admonished the prospective jurors and then jury, in accordance with Penal Code section 1122, that “it [was] their duty not to converse among themselves or with anyone else on any subject connected with the trial, or to form or express any opinion thereon until the cause [was] finally submitted to them,” and to avoid publicity relating to the case. It admonished them to immediately advise any person attempting to discuss the case with them that they could not do so, and to immediately report the matter if such person should persist. Barbara Durham was selected as one of the 12 jurors, and became the foreperson. On voir dire, she stated that she had not heard of the “Trailside Murders." She and the other 11 jurors evidently swore, in conformity with the oath prescribed by statute, that she would “well and truly try” the cause and “a true verdict render according to the evidence.” (Code Civ. Proc., former § 604, enacted 1872, repealed Stats. 1988, ch. 1245, § 7, p. 4155; accord, id., § 232, subd. (b).) During the guilt phase, evidence of the facts underlying the Santa Cruz crimes, except the Scaggs offenses, featured prominently, but evidence of the verdicts was not presented. The jury found Carpenter guilty on all charges, with the murders in the first degree, and found each of the allegations true. During the penalty phase, evidence of the facts underlying the Santa Cruz crimes, including the Scaggs offenses, but not the verdicts, was introduced. The jury returned a verdict of death, and the superior court imposed that sentence. Carpenter’s automatic appeal is pending in this court. II. The Habeas Corpus Proceeding Carpenter filed a petition for writ of habeas corpus in the San Diego Superior Court challenging the judgment in the Marin “Trailside Murder” case shortly after its rendition. He alleged that Juror Durham had committed prejudicial misconduct during trial. The matter was assigned to the trial judge, who issued an order to show cause why relief should not be granted. After a return—which challenged the jurisdiction of the superior court and denied the allegations of misconduct—and traverse were filed, the court ordered an evidentiary hearing. Carpenter presented extensive evidence, mainly through the testimony of Michael Lustig and Donna Duran. The respondent also presented extensive evidence, mainly through Juror Durham and her husband Ronald. The court characterized the evidentiary hearing as a “classic credibility contest” between Lustig and Duran on one side, and the Durhams on the other. It found Lustig’s testimony “credible ... in almost all respects,” and Duran’s credible in all respects. It doubted the testimony of the Durhams, and found that of Juror Durham, in its general denial of misconduct, perjurious. From all the evidence, the court determined that Juror Durham had committed misconduct by receiving information outside of court relating to the convictions and death sentence for the Santa Cruz crimes. By March 26, 1988, in the middle of the guilt phase, she had received the forbidden information from newspaper accounts, either directly or through her husband. Until at least March 26, 1988, the couple received delivery of a newspaper at their home. They had falsely stated in their original declarations that they had canceled their subscription around the opening of the guilt phase. Instead, they ordered cancellation on, or as of, March 26, 1988. At all relevant times, they were experiencing drinking problems and marital troubles. Ronald openly criticized the trial as a waste of time and money, having learned that Carpenter had already been convicted and sentenced to death for the Santa Cruz crimes. The “situation” was “very explosive,” presenting an “opportunity for a verbal battle between husband and wife while parties have been drinking.” “[0]n many occasions he apparently told her when she would come home from this trial, . . . T know so much more about this case than you do.’ [¶] . . .1 don’t know what would provoke that kind of response unless Mrs. Durham is somehow talking about aspects of the case.” He had the “opportunity ... to let his wife know in no uncertain terms that you’re just wasting your time on this trial because Mr. Carpenter has already got the death sentence and he’s been convicted of similar crimes.” The superior court also found that Juror Durham had committed misconduct by discussing the case pending before her and Carpenter’s Santa Cruz convictions and death sentence with nonjurors, including Lustig and Duran. On March 26, 1988, Lustig, Duran and others were having dinner at a resort in San Diego County. Lustig invited the Durhams, who were social acquaintances but not close friends, to his table. At Lustig’s table, Juror Durham initiated a five- or ten-minute conversation about the Marin case. She stated something like the jury was not supposed to know this, but Carpenter had already been convicted and sentenced to death for the Santa Cruz crimes. The court found Juror Durham to be “very outspoken,” and to have “no hesitancy talking about her marital problems” even “with a virtual stranger . . . . And . . . that’s somewhat similar to the fact that she would share with a stranger her confidential information about this case." “[S]he wanted to be the center of attention that night, and that kind of disclosure placed her in the center of attention with the Lustig[]” party. She admitted she had discussed the Marin case with Lustig and Duran, but denied revealing that she knew the forbidden information and knew it was forbidden. The court did not credit this. Having found misconduct, the court ordered a separate hearing on prejudice. At that hearing, the parties presented extensive argument but did not introduce new evidence. In a detailed ruling, the court found prejudice. It stated at the outset that it was applying the analysis of People v. Martinez (1978) 82 Cal.App.3d 1 [147 Cal.Rptr. 208], which held that whether a defendant has been prejudiced by a jury receiving evidence outside of court “depends upon whether the jury’s impartiality has been adversely affected, whether the prosecution’s burden of proof has been lightened and whether any asserted defense has been contradicted.” (Id. at p. 22.) The court analyzed prejudice at the penalty phase first, then at the guilt phase. Regarding penalty, the court analogized the receipt of the information to error under Caldwell v. Mississippi (1985) 472 U.S. 320 [86 L.Ed.2d 231, 105 S.Ct. 2633], which, the trial court stated, “held that it’s constitutionally impermissible to rest a death sentence on a determination made by a juror who has been led to believe that the responsibility for the defendant’s death rests elsewhere [than] in that juror’s determination.” The court found that the juror’s knowledge of the other death sentence “would serve to minimize her sense of responsibility in making the difficult and uncomfortable penalty determination,” and that therefore she “would have her impartiality compromised against the defendant by knowing that another jury of 12 has concluded that he is a person worthy of the death sentence and that would affect her decision.” The court found that the prosecution’s burden had been lightened because “there’s no way that she could have given that the same kind of consideration knowing on one hand that the defendant already had been sentenced to death by another jury.” Because of this, the court found that the prosecution had not rebutted the presumption of prejudice. The court then turned to the guilt phase. It stated that the evidence of guilt was “overwhelming,” but that because the defendant was entitled to trial by an unbiased jury, the “usual harmless error tests” did not apply. Therefore, “with respect to the guilt phase, to rebut the presumption of prejudice the People must show that Mrs. Durham remained impartial despite her knowledge of appellant’s other convictions for similar crimes and death sentence, and also, as the Martinez test states, the prosecution’s burden of proof was not lightened, and that no assertive defenses had been contradicted. That is a factual situation, and the likelihood of the same verdict despite the misconduct is of no consequence.” The court could not find “that the misconduct . . . and the information she received was innocuous or of a trivial nature. I would find that the extrajudicial information that caused her misconduct was inherently prejudicial.” “[T]he nature of the information was such that the juror’s impartiality could not be anything but adversely affected.” The fact the juror knew that defendant “was the kind of person that 12 other people . . . chose to sentence to death . . . could not but affect her determination of whether or not she could remain a fair and impartial juror as to this case and in evaluating the evidence and also his own testimony. So I definitely believe it affects her impartiality.” The court estimated that about two-thirds of the guilt phase evidence was directed to proving the Santa Cruz County crimes, and one-third to proving the Marin County crimes. It felt the improper knowledge was “highly prejudicial” and lightened the prosecution’s burden because of the “unique aspect of the case” that “it was conceded by the defense and argued by the prosecution that one person committed both the Santa Cruz and the Marin murders.” For the same reason, the court found that the juror’s knowledge undermined the defense that defendant “was not the trailside killer.” The court noted that it had done everything it could to keep the jury from learning of the earlier verdict. “And despite everything that was done by way of evidentiary rulings and the like, this is exactly the information that Mrs. Durham had.” For these reasons, the court “reluctantly” stated it had “no alternative than to grant the petition for writ of habeas corpus in its entirety . . . ."It further stated that “because of the gravity of the crimes themselves ... I would find beyond a reasonable doubt that any jury would have sentenced the defendant to the death penalty based upon the evidence presented and would also find that the evidence was so overwhelming with respect to defendant’s guilt that if . . . you could apply the harmless error standard to juror misconduct, I would find that her knowledge would be harmless beyond a reasonable doubt because of the overwhelming nature of the evidence in this case and as well as the overwhelming proof of the gravity of the aggravating circumstances in the penalty phase so completely outweighed and dominated the mitigation factors that the jury would make that result.” Because of this, the court felt that it was “an absolute travesty that such a result could happen to such a case." The court also stated its intent to inform the San Diego District Attorney and the Attorney General of the situation and its belief that “the matter should be reviewed for possible prosecution under Penal Code section 96 [stating the punishment for specified jury misconduct].” The superior court then granted the petition for writ of habeas corpus and vacated the judgment. The Director of Corrections appealed directly to this court. (Pen. Code, § 1506.) III. Discussion The Attorney General, representing the Director of Corrections, challenges both the jurisdiction of the superior court over this matter and its ruling on the merits. We address both contentions. A. Subject Matter Jurisdiction The Attorney General first argues the superior court did not have subject matter jurisdiction over the habeas corpus proceeding challenging the Marin “Trailside Murder" judgment because the automatic appeal from the same judgment is pending in this court. We disagree. Section 10 of article VI of the California Constitution (hereafter article VI, section 10) provides in pertinent part: “The Supreme Court, courts of appeal, superior courts, and their judges have original jurisdiction in habeas corpus proceedings.” This provision grants original subject matter jurisdiction over habeas corpus proceedings concurrently to the superior court, the Court of Appeal, and this court. (E.g., France v. Superior Court (1927) 201 Cal. 122, 131 [255 P. 815, 52 A.L.R. 869] [decided under former §§ 4 & 5 of art. VI of Cal. Const., which were the substantially similar predecessors of present art. VI, § 10]; People v. Mayfield (1993) 5 Cal.4th 220, 224-225 [following France under present art. VI, § 10].) Nothing in article VI, section 10, or any other provision of law, denies the superior court of subject matter jurisdiction over habeas corpus proceedings when the challenged judgment is pending on appeal before an appellate court or even when, as here, a judgment of death is pending on automatic appeal before this court. None of the authorities the Attorney General cites holds to the contrary. As to his policy arguments, the superior court’s original, concurrent subject matter jurisdiction over habeas corpus proceedings is a “policy” declared in the California Constitution. It must be implemented by the judiciary. We agree with the Attorney General that “[c]apital cases are different.” They are exclusively within our appellate jurisdiction. (Cal. Const., art. VI, § 11.) But they are not exclusively within our habeas corpus jurisdiction. To the extent that the Attorney General quarrels with the superior court’s determination that its exercise of subject matter jurisdiction was appropriate in view of “the interests of justice, judicial economy, and the avoidance of potentially prejudicial delay to both parties,” we also disagree. This is not to say that the superior court may exercise its subject matter jurisdiction over habeas corpus proceedings wherever such jurisdiction extends. It does not have “the power to interfere with the appellate jurisdiction of either [this court or the Court of Appeal] in matters pending before said appellate courts . . . .” (France v. Superior Court, supra, 201 Cal. at p. 132; accord, People v. Mayfield, supra, 5 Cal.4th at p. 225.) There was no such interference here. On habeas corpus, the superior court entertained only the claim of juror misconduct that did not appear of record. In the exercise of our appellate jurisdiction, we could not consider that point. Appellate jurisdiction is limited to the four comers of the record on appeal (e.g., People v. Merriam (1967) 66 Cal.2d 390, 396-397 [58 Cal.Rptr. 1, 426 P.2d 161], disapproved on another point, People v. Rincon-Pineda (1975) 14 Cal.3d 864, 882 [123 Cal.Rptr. 119, 538 P.2d 247, 92 AX.R.3d 845])—which, in this case, does not include the evidence of misconduct. We thus conclude the superior court had jurisdiction over this matter. B. Prejudicial Juror Misconduct The Attorney General does not challenge, and we accept, the superior court’s findings of historical fact, which resolved a credibility dispute. The power to judge the credibility of witnesses and to resolve conflicts in the testimony is vested in the trial court, and its findings of fact, express or implied, must be upheld if supported by substantial evidence. (People v. Leyba (1981) 29 Cal.3d 591, 596-597 [174 Cal.Rptr. 867, 629 P.2d 961].) Here the court expressly resolved the conflicts in the testimony in Carpenter’s favor, and we find substantial evidence supports these factual findings. In essence, during the trial, the juror in question learned forbidden information but did not report it, then told some nonjurors at a party that the jurors were not supposed to know, but Carpenter had already been convicted and sentenced to death for the Santa Cruz crimes, and then lied about it when confronted after trial. The Attorney General also does not deny that these facts establish misconduct. They clearly do. It is improper for a juror to receive information outside of court about the pending case, and to discuss the case with nonjurors. (E.g., In re Hitchings (1993) 6 Cal.4th 97, 116-118 [24 Cal.Rptr.2d 74, 860 P.2d 466]; People v. Holloway (1990) 50 Cal.3d 1098, 1108 [269 Cal.Rptr. 530, 790 P.2d 1327].) But he argues the court erred in its finding that the misconduct was prejudicial. We agree. In considering this question, we first review the applicable law, then apply it to this case. 1. The Applicable Law Carpenter relies heavily on a trio of recent decisions by this court which state the test for determining prejudice from juror misconduct. (In re Hitchings, supra, 6 Cal.4th 97; People v. Holloway, supra, 50 Cal.3d 1098; People v. Marshall (1990) 50 Cal.3d 907 [269 Cal.Rptr. 269, 790 P.2d 676].) We will address these and other California cases in due course, but we begin by discussing some decisions of the United States Supreme Court that will help place this issue into context, and point the way to the proper application of the test we have established. The first, Smith v. Phillips (1982) 455 U.S. 209 [71 L.Ed.2d 78, 102 S.Ct. 940], involved facts that in some respects are more troubling than those here. The defendant was convicted by jury of crimes in state court. During the trial, one of the actual jurors applied “for employment as a major felony investigator in the District Attorney’s Office.” (Id. at p. 212 [71 L.Ed.2d at p. 83].) When the defendant learned of this after trial, he unsuccessfully moved to set aside the verdict. The trial court found that the employment application “ ‘was indeed an indiscretion,’ ” but it did not indicate prejudice against the defendant or an inability to decide guilt or innocence “ ‘solely on the evidence.’ ” (Id. at pp. 213-214 [71 L.Ed.2d at p. 84].) The high court found no constitutional infirmity in the verdict despite the obvious inherent motivation the job applicant may have had to reach a verdict favorable to the prospective employer. It rejected the argument that “the law must impute bias to jurors” in that position, stating that the “Court has long held that the remedy for allegations of juror partiality is a hearing in which the defendant has the opportunity to prove actual bias.” (Smith v. Phillips, supra, 455 U.S. at p. 215 [71 L.Ed.2d at p. 85], italics added.) The court reviewed prior decisions and concluded that they “demonstrate that due process does not require a new trial every time a juror has been placed in a potentially compromising situation. Were that the rule, few trials would be constitutionally acceptable. The safeguards of juror impartiality, such as voir dire and protective instructions from the trial judge, are not infallible; it is virtually impossible to shield jurors jrom every contact or influence that might theoretically affect their vote. Due process means a jury capable and willing to decide the case solely on the evidence before it, and a trial judge ever watchful to prevent prejudicial occurrences and to determine the effect of such occurrences when they happen.” (Id. at p. 217 [71 L.Ed.2d at p. 86], italics added.) In Rushen v. Spain (1983) 464 U.S. 114 [78 L.Ed.2d 267, 104 S.Ct. 453], the court considered the effect on a verdict of improper ex parte communications between the trial court and jurors during a lengthy trial. It took a similarly pragmatic approach. “Our cases recognize that the right to personal presence at all critical stages of the trial and the right to counsel are fundamental rights of each criminal defendant. [Fn. omitted.] ‘At the same time and without detracting from the fundamental importance of [these rights], we have implicitly recognized the necessity for preserving society’s interest in the administration of criminal justice. Cases involving [such constitutional] deprivations are [therefore] subject to the general rule that remedies should be tailored to the injury suffered . . . and should not unnecessarily infringe on competing interests.’ [Citations.]” (Id. at pp. 117-118 [78 L.Ed.2d at pp. 272-273].) The high court stated, “There is scarcely a lengthy trial in which one or more jurors do not have occasion to speak to the trial judge about something, whether it relates to a matter of personal comfort or to some aspect of the trial. The . . . conclusion that an unrecorded ex parte communication between trial judge and juror can never be harmless error ignores these day-to-day realities of courtroom life and undermines society’s interest in the administration of criminal justice.” (Rushen v. Spain, supra, 464 U.S. at pp. 118-119 [78 L.Ed.2d at p. 273], quoted with approval in People v. Wright (1990) 52 Cal.3d 367, 402-403 [276 Cal.Rptr. 731, 802 P.2d 221], italics added.) As an example, the court noted that “we have refused, on facts more troublesome than these, to find inherent bias in a verdict when a state trial court determined ‘beyond a reasonable doubt’ that a juror’s out-of-court action did not influence the verdict.” (Rushen v. Spain, supra, 464 U.S. at p. 119, fn. 3 [78 L.Ed.2d at p. 273], citing Smith v. Phillips, supra, 455 U.S. 209.) McDonough Power Equipment, Inc. v. Greenwood (1984) 464 U.S. 548 [78 L.Ed.2d 663, 104 S.Ct. 845] involved a juror who failed to disclose certain information during voir dire. In holding that a new trial is not required “unless the juror’s failure to disclose denied respondents their right to an impartial jury” (id. at p. 549 [78 L.Ed.2d at p. 667]), the high court noted, “Trials are costly, not only for the parties, but also for the jurors performing their civic duty and for society which pays the judges and support personnel who manage the trials. It seems doubtful that our judicial system would have the resources to provide litigants with perfect trials, were they possible, and still keep abreast of its constantly increasing caseload.” (Id. at p. 553 [78 L.Ed.2d at p. 669].) A decision last term, Romano v. Oklahoma (1994) 512 U.S. _ [129 L.Ed.2d 1, 114 S.Ct. 2004], is significant given the trial court’s characterization of the misconduct here as error under Caldwell v. Mississippi, supra, 472 U.S. 320. In Romano, the petitioner, like Carpenter, was charged and tried separately for separate capital offenses. In the first trial, the jury found the petitioner guilty of murder and sentenced him to death. A different jury then convicted him of a second murder and also sentenced him to death. During the sentencing phase of the second trial, evidence of the first murder was presented. Additionally, evidence of the first conviction and death sentence was also presented to the jury—erroneously but harmlessly, the state appellate court later held. While appeal of the second judgment was pending, the first conviction was reversed on direct appeal. After the state court affirmed the second judgment, the high court granted certiorari and then affirmed. Distinguishing and limiting Caldwell v. Mississippi, supra, 472 U.S. 320, the court did “not believe that the admission of evidence regarding petitioner’s prior death sentence affirmatively misled the jury regarding its role in the sentencing process so as to diminish its sense of responsibility. The admission of this evidence, therefore, did not contravene the principle established in Caldwell.” (Romano v. Oklahoma, supra, 512 U.S. at p._ [129 L.Ed.2d at p. 11].) The court also rejected other constitutional challenges to the evidence. Regarding a due process challenge under the Fourteenth Amendment, the court stated that the “relevant question in this case ... is whether the admission of evidence regarding petitioner’s prior death sentence so infected the sentencing proceeding with unfairness as to render the jury’s imposition of the death penalty a denial of due process.” (Romano v. Oklahoma, supra, 512 U.S. at p__[129 L.Ed.2d at p. 13].) It found no such unfairness. “[I]f the jurors followed the trial court’s instructions, which we presume they did [citation], this evidence should have had little—if any—effect on their deliberations. Those instructions clearly and properly described the jurors’ paramount role in determining petitioner’s sentence, and they also explicitly limited the jurors’ consideration of aggravating factors to the four which the State sought to prove. Regardless of the evidence as to petitioner’s death sentence in the [first] case, the jury had sufficient evidence to justify its conclusion that these four aggravating circumstances existed. ... In short, the instructions did not offer the jurors any means by which to give effect to the evidence of petitioner’s sentence in the [first] murder, and the other relevant evidence presented by the State was sufficient to justify the imposition of the death sentence in this case.” {Id. at p._[129 L.Ed.2d at pp. 13-14].) In a discussion particularly pertinent here, the high court concluded, “Even assuming that the jury disregarded the trial court’s instructions and allowed the evidence of petitioner’s prior death sentence to influence its decision, it is impossible to know how this evidence might have affected the jury. It seems equally plausible that the evidence could have made the jurors more inclined to impose a death sentence, or it could have made them less inclined to do so. Either conclusion necessarily rests upon one’s intuition. To hold on the basis of this record that the admission of evidence relating to petitioner’s sentence in the [first] case rendered petitioner’s sentencing proceeding for the [second] murder fundamentally unfair would thus be an exercise in speculation, rather than reasoned judgment.” (Romano v. Oklahoma, supra, 512 U.S. at p__[129 L.Ed.2d at p. 14].) With these decisions as a backdrop, we now consider the cases on which Carpenter relies. In People v. Marshall, supra, 50 Cal.3d at pages 949-950, one juror told the other jurors during deliberations that he had a law enforcement background, and stated legal principles that were both extraneous and erroneous. We found this to be misconduct giving rise to a presumption of prejudice, but also stated, “The jury system is an institution that is legally fundamental but also fundamentally human. Jurors bring to their deliberations knowledge and beliefs about general matters of law and fact that find their source in everyday life and experience. That they do so is one of the strengths of the jury system. It is also one of its weaknesses: it has the potential to undermine determinations that should be made exclusively on the evidence introduced by the parties and the instructions given by the court. Such a weakness, however, must be tolerated. ‘[I]t is an impossible standard to require . . . [the jury] to be a laboratory, completely sterilized and freed from any external factors.’ [Citation.] Moreover, under that ‘standard’ few verdicts would be proof against challenge.” (Id. at p. 950.) We then stated the test to apply in determining whether juror misconduct requires the judgment be set aside: “A judgment adverse to a defendant in a criminal case must be reversed or vacated ‘whenever ... the court finds a substantial likelihood that the vote of one or more jurors was influenced by exposure to prejudicial matter relating to the defendant or to the case itself that was not part of the trial record on which the case was submitted to the jury.’ [Citations.] . . . [¶] ‘The ultimate issue of influence on the juror is resolved by reference to the substantial likelihood test, an objective standard. In effect, the court must examine the extrajudicial material and then judge whether it is inherently likely to have influenced the juror.’ [Citation.]” (People v. Marshall, supra, 50 Cal.3d at pp. 950-951, italics added.) We noted that this prejudice analysis is “different from, and indeed less tolerant than, ‘harmless-error analysis’ for ordinary error at trial. The reason is as follows. Any deficiency that undermines the integrity of a trial—which requires a proceeding at which the defendant, represented by counsel, may present evidence and argument before an impartial judge and jury—introduces the taint of fundamental unfairness and calls for reversal without consideration of actual prejudice. [Citation.] Such a deficiency is threatened by jury misconduct. When the misconduct in question supports a finding that there is a substantial likelihood that at least one juror was impermissibly influenced to the defendant’s detriment, we are compelled to conclude that the integrity of the trial was undermined: under such circumstances, we cannot conclude that the jury was impartial. By contrast, when the misconduct does not support such a finding, we must hold it nonprejudicial.” {Id. at p. 951.) Applying this test, we found the misconduct harmless. (People v. Marshall, supra, 50 Cal.3d at pp. 951-952.) In People v. Holloway, supra, 50 Cal.3d 1098, one juror improperly read a newspaper article during trial stating that the defendant had been on parole from prison for assaulting a woman with a hammer. This impropriety was not discovered until after the guilt phase verdicts. We noted that such misconduct gives rise to a presumption of prejudice, and discussed the significance of that presumption: “ ‘[W]hen misconduct of jurors is shown, it is presumed to be injurious to defendant, unless the contrary appears.' [Citation.] We have long recognized the reason for this rule: ‘A juror is not allowed to say: “I acknowledge to grave misconduct. I received evidence without the presence of the court, but those matters had no influence upon my mind when casting my vote in the jury-room.” The law, in its wisdom, does not allow a juror to purge himself in that way. . . . “But, where . . . without any fault of either party . . . , a paper was communicated to the jury which might have influenced their minds, the testimony of the jurors is [not admissible] to show whether it did or did not influence their deliberations and decision. A juryman may testify to any facts bearing upon the question of the existence of the disturbing influence, but he cannot be permitted to testify how far that influence operated upon his mind.” ’ (People v. Stokes [(1894) 103 Cal. 193, 196-197 (37 P. 207)].) That principle is now embodied in Evidence Code section 1150.” (People v. Holloway, supra, 50 Cal.3d at pp. 1108-1109, italics added; see also People v. Cooper (1991) 53 Cal.3d 771, 835-836 [281 Cal.Rptr. 90, 809 P.2d 865] [“When a person violates his oath as a juror, doubt is cast on that person’s ability to otherwise perform his duties.”].) The defendant need not affirmatively prove the jury’s deliberations were improperly affected by the misconduct, for that cannot be done under Evidence Code section 1150 and the authority cited in People v. Holloway, supra, 50 Cal.3d at pages 1108-1109. Therefore, “ ‘The presumption of prejudice is an evidentiary aid to those parties who are able to establish serious misconduct of a type likely to have had an effect on the verdict or which deprived the complaining party of thorough consideration of his case, yet who are unable to establish by a preponderance of the evidence that actual prejudice occurred. The law thus recognizes the substantial barrier to proof of prejudice which Evidence Code section 1150 erects, and it seeks to lower that barrier somewhat.’ (Hasson v. Ford Motor Co. (1982) 32 Cal.3d 388, 416 [185 Cal.Rptr. 654, 650 P.2d 1171].)” (Id. at p. 1109.) We then applied the test of People v. Marshall, supra, 50 Cal.3d 907, and found the misconduct prejudicial. “The content of the article was extremely prejudicial; it revealed information about defendant’s prior criminal conduct that the court had ruled inadmissible because of its potential for prejudice. The court and counsel had gone to great lengths to avoid having the jury learn of defendant’s prior conviction for having assaulted a woman with a hammer. Their efforts were to no avail as to one juror—a fact that they did not learn until after it was too late to take any curative steps. [¶] . . . [¶] . . . [T]he defense went through the entire guilt phase thinking that the jury was unaware of defendant’s prior record when in fact one juror had such knowledge. We cannot say at this point that [the juror’s] improper knowledge had no impact. . . . [¶] Under the circumstances, we are unable to conclude that the presumption of prejudice has been rebutted.” (People v. Holloway, supra, 50 Cal.3d at pp. 1110-1111.) We also made clear that even one biased juror requires overturning the verdict. “Defendant was entitled to be tried by 12, not 11, impartial and unprejudiced jurors. ‘Because a defendant charged with crime has a right to the unanimous verdict of 12 impartial jurors [citation], it is settled that a conviction cannot stand if even a single juror has been improperly influenced.’ [Citations.]” (People v. Holloway, supra, 50 Cal.3d at p. 1112.) We did not hold, however, that the improper receipt of any potentially prejudicial information required reversal. “Opr conclusion might have been different ... if the information improperly obtained . . . had been less prejudicial.” (People v. Holloway, supra, 50 Cal.3d at pp. 1111-1112.) Our most recent decision involving juror misconduct was In re Hitchings, supra, 6 Cal.4th 97. There, timing voir dire, a juror intentionally concealed knowledge she had about the case and, during the guilt trial, she made statements to a nonjuror indicating that she already believed the defendant was guilty. (Id. at pp. 116, 117.) This was clearly misconduct giving rise to the presumption of prejudice. “This presumption of prejudice ‘ “may be rebutted by an affirmative evidentiary showing that prejudice does not exist or by a reviewing court’s examination of the entire record to determine whether there is a reasonable probability of actual harm to the complaining party [resulting from the misconduct]. . . (Id. at p. 119, quoting People v. Miranda (1987) 44 Cal.3d 57, 117 [241 Cal.Rptr. 594, 744 P.2d 1127], which itself quoted Hasson v. Ford Motor Co. (1982) 32 Cal.3d 388, 417 [185 Cal.Rptr. 654, 650 P.2d 1171], italics added.) We found the presumption had not been rebutted because the evidence showed it to be “ ‘reasonably probable’ [the juror] had prejudged the case.” (In re Hitchings, supra, 6 Cal.4th at p. 121.) To summarize, when misconduct involves the receipt of information from extraneous sources, the effect of such receipt is judged by a review of the entire record, and may be found to be nonprejudicial. The verdict will be set aside only if there appears a substantial likelihood of juror bias. Such bias can appear in two different ways. First, we will find bias if the extraneous material, judged objectively, is inherently and substantially likely to have influenced the juror. (E.g., People v. Holloway, supra, 50 Cal.3d at pp. 1110-1112; People v. Marshall, supra, 50 Cal.3d at pp. 951-952.) Second, we look to the nature of the misconduct and the surrounding circumstances to determine whether it is substantially likely the juror was actually biased against the defendant. (E.g., In re Hitchings, supra, 6 Cal.4th at p. 121.) The judgment must be set aside if the court finds prejudice under either test. The first of these tests is analogous to the general standard for harmless-error analysis under California law. Under this standard, a finding of “inherently” likely bias is required when, but only when, the extraneous information was so prejudicial in context that its erroneous introduction in the trial itself would have warranted reversal of the judgment. Application of this “inherent prejudice” test obviously depends upon a review of the trial record to determine the prejudicial effect of the extraneous information. But a finding that the information was “harmless” by appellate standards, and thus not “inherently” biasing, does not end the inquiry. Ultimately, the test for determining whether juror misconduct likely resulted in actual bias is “different from, and indeed less tolerant than,” normal harmless error analysis, for if it appears substantially likely that a juror is actually biased, we must set aside the verdict, no matter how convinced we might be that an unbiased jury would have reached the same verdict. (People v. Marshall, supra, 50 Cal.3d at p. 951.) A biased adjudicator is one of the few “structural defects in the constitution of the trial mechanism, which defy analysis by ‘harmless-error’ standards.” (Arizona v. Fulminante (1991) 499 U.S. 279, 309 [113 L.Ed.2d 302, 331, 111 S.Ct. 1246]; see also Rose v. Clark (1986) 478 U.S. 570, 577-578 [92 L.Ed.2d 460, 470-471, 106 S.Ct. 3101]; Morgan v. Illinois (1992) 504 U.S. 719, 729 [119 L.Ed.2d 492, 502-503, 112 S.Ct. 2222, 2229-2230]; People v. Cahill (1993) 5 Cal.4th 478, 501-502 [20 Cal.Rptr.2d 582, 853 P.2d 1037].) Thus, even if the extraneous information was not so prejudicial, in and of itself, as to cause “inherent” bias under the first test, the totality of the circumstances surrounding the misconduct must still be examined to determine objectively whether a substantial likelihood of actual bias nonetheless arose. Under this second, or “circumstantial,” test, the trial record is not a dispositive consideration, but neither is it irrelevant. All pertinent portions of the entire record, including the trial record, must be considered. “The presumption of prejudice may be rebutted, inter alia, by a reviewing court’s determination, upon examining the entire record, that there is no substantial likelihood that the complaining party suffered actual harm.” (People v. Hardy (1992) 2 Cal.4th 86, 174 [5 Cal.Rptr.2d 796, 825 P.2d 781], italics added.) In an extraneous-information case, the “entire record” logically bearing on a circumstantial finding of likely bias includes the nature of the juror’s conduct, the circumstances under which the information was obtained, the instructions the jury received, the nature of the evidence and issues at trial, and the strength of the evidence against the defendant. For example, the stronger the evidence, the less likely it is that the extraneous information itself influenced the verdict. An example is provided in Hasson v. Ford Motor Co., supra, 32 Cal.3d at page 417, where we found the presumption of prejudice had been rebutted, in part because “[t]here was overwhelming proof’ in support of the verdict. We emphasize that before a unanimous verdict is set aside, the likelihood of bias under either test must be substantial. As indicated in the high court decisions discussed above, the criminal justice system must not be rendered impotent in quest of an ever-elusive perfection. The jury system is fundamentally human, which is both a strength and a weakness. (People v. Marshall, supra, 50 Cal.3d at p. 950.) Jurors are not automatons. They are imbued with human frailties as well as virtues. If the system is to function at all, we must tolerate a certain amount of imperfection short of actual bias. To demand theoretical perfection from every juror during the course of a trial is unrealistic. If the court concludes it is substantially likely the outside information affected the verdict, or that the juror was actually biased, the verdict must be set aside. If not, “society’s interest in the administration of criminal justice” (Rushen v. Spain, supra, 464 U.S. at p. 119 [78 L.Ed.2d at pp. 273-274]) must be vindicated, and the judgment preserved. It is not enough that the juror was “placed in a potentially compromising situation,” for then “few trials would be constitutionally acceptable.” (Smith v. Phillips, supra, 455 U.S. at p. 217 [71 L.Ed.2d at p. 86].) 2. The Law Applied to This Case In finding penalty phase prejudice, the trial court analogized the misconduct and resultant extraneous information to error under Caldwell v. Mississippi, supra, 472 U.S. 320. For the reasons stated in Romano v. Oklahoma, supra, 512 U.S._ [129 L.Ed.2d 1], this is incorrect, at least without considering the instructions the jury was given and other relevant information from the trial. (In fairness to the trial court, we note that Romano long postdates its decision.) The court also erred in the rest of its determination and in its finding of guilt phase prejudice. As discussed in part II, ante, the court found that the extraneous information was inherently prejudicial in and of itself without reference to the rest of the record. It stated the evidence of guilt (as well as that supporting the penalty determination) was “overwhelming,” but felt legally precluded from considering this evidence. This is incorrect. To be sure, once actual bias is found, the strength of the evidence is irrelevant; the verdict must be set aside. But such evidence is relevant in determining bias in the first place. Contrary to the dispositive finding of the court below, if the evidence was truly overwhelming, the extraneous information cannot be considered “inherently” prejudicial. This is especially true since evidence of most of the Santa Cruz County crimes was presented to the jury. All the juror learned out of court was the verdict of the first jury. We also find that the surrounding circumstances do not necessarily reveal a substantial likelihood the juror actually was impermissibly influenced by the outside information. The trial court did not make any credibility-based finding that this specific juror was biased, only that the information would have improperly influenced any juror. Without minimizing the seriousness of the misconduct here, and “ ‘without detracting from the fundamental importance’ ” of the rights at stake (Rushen v. Spain, supra, 464 U.S. at pp. 117-118 [78 L.Ed.2d at p. 273]), on the basis of the habeas corpus record alone, we do not find a substantial likelihood the juror was biased or that the extraneous information impermissibly influenced her to the defendant’s detriment. During a long and highly publicized trial, the court and parties attempted to prevent the jury from learning of the verdict in the previous trial (although not from hearing evidence of most of the other crimes themselves). Despite these efforts, one juror learned the truth. Although unfortunate, this is hardly shocking, and does not itself show bias. Just as there is “scarcely a lengthy trial in which one or more jurors do not have occasion to speak to the trial judge” (Rushen v. Spain, supra, 464 U.S. at p. 118 [78 L.Ed.2d at p. 273]), so too it is virtually inevitable that in a trial such as this some secrets cannot be kept. “The safeguards of juror impartiality ... are not infallible; it is virtually impossible to shield jurors from every contact or influence that might theoretically affect their vote.” (Smith v. Phillips, supra, 455 U.S. at p. 217 [71 L.Ed.2d at p. 86].) The juror also failed to report what she had learned, as she should have. But to the extent this was misconduct, it was also passive. Having learned what she should not, she chose—improperly to be sure—to keep it to herself. But this alone does not show bias. Many jurors, in the middle of a long and notorious trial, might, for many reasons unrelated to bias, be reluctant to go forward and actively inject themselves into the proceedings. For example, a juror might not attach the same importance to a particular piece of information as do the parties. The juror also told nonjurors both what she knew and that she knew it was forbidden, and later, after the verdict, denied the misconduct. But it does not follow that she thereby failed to base her verdict solely on the evidence. Telling nonjurors what she knew could not itself have prejudiced defendant. Learning the secret during the long and publicized trial (and then not reporting it) is one thing. Actually using the forbidden information—rather than basing the verdict on the evidence—is quite different. The juror did not suggest that she would consider the extraneous information in reaching her verdict, or that the verdict would be based on anything other than what the trial court characterized as the “overwhelming” evidence. Moreover, the juror did not discuss the defendant’s guilt or innocence, and said nothing suggesting she had prejudged the case. Her statement that she was not supposed to know the information she had obtained, although revealing a consciousness of guilt in one sense, also showed that she was aware the knowledge was not supposed to influence her verdict. It does not indicate that she did what she knew was not allowed. Similarly, the fact the juror covered up after the verdict when she was challenged in order to protect herself, although certainly improper, does not show bias during the trial, deliberations, and verdict. We also note the lack of evidence that the juror told any fellow jurors, as distinct from nonjurors, what she had learned. Carpenter argues that because prejudice is presumed, we must assume she did tell the other jurors absent affirmative evidence that she did not. That is incorrect. Although prejudice is presumed once misconduct has been established, the initial burden is on defendant to prove the misconduct. (People v. Marshall, supra, 50 Cal.3d at p. 949.) We will not presume greater misconduct than the evidence shows. On this record, we must assume the misconduct extended to learning the information and revealing it to nonjurors, but not to revealing it to other jurors. Carpenter argues this does not matter because even one improperly influenced juror is enough to overturn the verdict. This is correct once bias is established, but the exact nature of the misconduct is highly relevant to the initial determination of bias, which is based on all the surrounding circumstances. Indeed, in In re Stankewitz (1985) 40 Cal.3d 391, 399-400 [220 Cal.Rptr. 382, 708 P.2d 1260], we relied heavily on the fact a juror told others what he (erroneously) thought he knew in finding prejudicial misconduct. The fact the juror here did not reveal her knowledge to the rest of the jury is not alone dispositive, but it is also not irrelevant. Rather, it is probative in two important respects. First, it tends to negate the inference the juror was biased; a biased juror would likely have told other jurors what she had learned. Second, it tends to show the juror intended the forbidden information not to influence the verdict. The fact that the respondent below did not present affirmative evidence showing there was no prejudice also is not dispositive. The presumption of prejudice may be rebutted by an affirmative evidentiary showing “or by a reviewing court’s examination of the entire record to determine whether there is a reasonable probability of actual harm to the complaining party resulting from the misconduct.” (Hasson v. Ford Motor Co., supra, 32 Cal.3d at p. 417, italics added; see also People v. Hardy, supra, 2 Cal.4th at p. 176 [the presumption of prejudice was rebutted “by the evidence” of the trial itself].) As discussed in People v. Holloway, supra, 50 Cal.3d at pages 1108-1109, the presumption of prejudice merely excuses the defendant from affirmatively proving prejudice when that cannot be done. The presumption prevails “ ‘unless the contrary appears.’ ” (Id. at p. 1108.) If a juror applying for employment with the office of one of the attorneys in a case does not compel a finding of bias, as in Smith v. Phillips, supra, 455 U.S. 209, so too the evidence of the habeas corpus evidentiary hearing of this case does not itself compel a finding of bias. Our recent trio of cases is distinguishable. We found the misconduct harmless in People v. Marshall, supra, 50 Cal.3d 907. In In re Hitchings, supra, 6 Cal.4th 97, the juror had concealed information during jury selection, which did not occur here. We also found a reasonable probability that the juror had “prejudged the case.” (Id. at p. 121.) There was no evidence of prejudging in this case. People v. Holloway, supra, 50 Cal.3d 1098, is factually more similar, but also distinguishable. There, evidence of the other crimes was not presented at all, and the extrinsic information was particularly prejudicial. As we noted there, the outcome might have been different had the information “been less prejudicial.” (Id. at p. 1112.) Here, a review of the entire record may show the extrinsic information was not prejudicial. IV. Disposition We conclude that, on the basis of the habeas corpus record, the only one before us in this cause, Carpenter is not entitled to relief, and the court below erred in finding otherwise. The court thus erred in setting aside the judgment of death, which error was prejudicial to the appealing party, in effect the People. We therefore reverse the judgment granting the petition for writ of habeas corpus. We must now decide the precise disposition. We find that, although an examination of the entire record in this habeas corpus cause, including the evidence presented at the habeas corpus hearing, suffices to find that the court erroneously set aside the judgment in the underlying action, that record is not sufficient to decide whether Carpenter could ever be entitled to relief. This latter determination requires an examination, not only of the record in this cause, but also the record in the underlying appeal, which is not before us in this matter. As discussed above, in determining prejudice to Carpenter, the record of the underlying trial, in addition to the habeas record, must be consulted. The trial court felt precluded from doing this. We could remand the matter to the court to make a new ruling. But, although determinations during trial whether a juror is biased and should be excused are entitled to deferential treatment by a reviewing court (People v. McPeters (1992) 2 Cal.4th 1148, 1175 [9 Cal.Rptr.2d 834, 832 P.2d 146]), as are credibility-based factual determinations by the trial court (In re Hitchings, supra, 6 Cal.4th at p. 109), neither of these circumstances suggests a remand here. The trial court did resolve the factual conflict in Carpenter’s favor, which we fully accept. As we have seen, however, those factual findings do not themselves compel a finding of prejudice. Moreover, posttrial prejudice is a mixed question of law and fact ultimately determined by the “reviewing court.” (People v. Hardy, supra, 2 Cal.4th at p. 174; see, e.g., People v. Holloway, supra, 50 Cal.3d 1098.) Because there is now a full factual record regarding the misconduct with all conflicts in the evidence resolved and with the relevant historical facts found, little would be gained by a remand. At this point, the question is for our independent determination. On the other hand, we have not yet fully reviewed the entire record. To be sure, we have carefully considered the habeas corpus record, and have determined that it alone does not entitle Carpenter to relief; the trial court erred in finding otherwise. But the record of the trial which is not before us in this cause, is different, and must be considered before the merits of Carpenter’s underlying claim can be finally determined. The record in the automatic appeal promises to be massive but has not yet been certified. In his habeas corpus petition, Carpenter requested the superior court to judicially notice its records in the underlying trial, which it granted, at least impliedly. (Evid. Code, § 452, subd. (d).) On appeal, the Attorney General asks us to judicially notice those records. We grant that request (Evid. Code, § 459, subd. (a)), limited to noncontroversial facts regarding the trial referred to in this opinion that are also reflected in the habeas corpus record. But, although judicial notice properly gives us a general idea of what the trial was about, because it is uncertified, we find it inadequate to the task of making a final determination of prejudice to Carpenter. Therefore, we cannot, and do not, consider it for that purpose at this time. The trial court stated the evidence in support of the verdicts was “overwhelming,” but also cited the role the Santa Cruz crimes played in the trial. Moreover, as suggested, for example, in Romano v. Oklahoma, supra, 512 U.S. at page_[129 L.Ed.2d at pages 13-14], the precise jury instructions may be pertinent. The record may be relevant in other ways. We cannot now effectively examine the appellate record to confidently review these matters and decide whether Carpenter was prejudiced. Because of this, it seems prudent not to make a definitive determination of this question at this time, but to reserve it pending a cause in which the appellate record, as well as the record in this cause, is before us. To resolve this conundrum—which potentially exists in any appeal from a grant of habeas corpus relief such as this—we will reverse the trial court’s granting of relief, and provisionally deny the petition at this time. But the denial is without prejudice to Carpenter filing a new petition in this court raising the issue in a manner consistent with this opinion, and based upon the combined records of the habeas corpus proceeding and the underlying trial. Any new petition, which may or may not contain additional claims for relief, would be filed in the same manner, and be subject to the same rules, as any other petition in a death penalty case. We will then consider any such petition after the appellate record has been certified. Accordingly, the judgment of the superior court granting the petition for writ of habeas corpus is reversed, and the petition is denied without prejudice to Carpenter’s filing a new petition in this court in a manner consistent with this opinion. Baxter, J., George, J., and Werdegar, J., concurred. MOSK, J. I dissent. This is the easy case that makes bad law. In their efforts to find undisputed and serious juror misconduct harmless, the majority conduct an analysis that is specious and fabricate a disposition that is wrong. I refuse to follow. I In the Santa Cruz Superior Court, the People accused David Joseph Carpenter of certain offenses committed in that county in the spring of 1981. Specifically, they charged him in five counts with: (1) the murder of Ellen Marie Hansen, with allegations, for death eligibility, that he acted under the special circumstances of felony-murder rape, lying in wait, and multiple murder; (2) the attempted rape of Hansen; (3) the attempted murder of Steven Russell Haertle, with allegations, for enhancement of sentence, that he personally used a firearm and intentionally inflicted great bodily injury; (4) the murder of Heather Scaggs, with allegations that he acted under the special circumstances of felony-murder rape and multiple murder; and (5) the rape of Scaggs. Carpenter pleaded not guilty to the charges and denied the allegations. After change of venue to Los Angeles County because of pretrial publicity, the superior court called the cause to trial before a jury. After the guilt phase, the jury returned verdicts of guilty as to each of the charges, fixing each of the murders at the first degree, and also returned findings of true as to each of the allegations. After the penalty phase, it returned a verdict of death for each of the murders. The superior court rendered judgment accordingly. For each of the murders, it imposed a sentence of death. For the related offenses, it suspended imposition of sentence. Our clerk then docketed an automatic appeal. Subsequently, in San Diego Superior Court, after change of venue from Marin County because of pretrial publicity, the People accused Carpenter of certain offenses committed in the latter county in the fall of 1980. Specifically, they charged him in eight counts with: (1) the murder of Cynthia Toshiko Moreland, with an allegation that he personally used a firearm; (2) the murder of Richard Edward Stowers, with an allegation that he personally used a firearm; (3) the murder of Anne Evelyn Alderson, with allegations that he acted under the special circumstance of felony-murder rape and that he personally used a firearm; (4) the rape of Alderson, with an allegation that he personally used a firearm; (5) the murder of Diane Marie O’Connell, with allegations that he acted under the special circumstance of felony-murder rape and that he personally used a firearm; (6) the attempted rape of O’Connell, with an allegation that he personally used a firearm; (7) the murder of Shauna Catherine May, with allegations that he acted under the special circumstance of felony-murder rape and that he personally used a firearm; and (8) the rape of May, with an allegation that he personally used a firearm; there was also an allegation, separate and independent from any individual count, that he committed the five charged murders under the special circumstance of multiple murder. Carpenter pleaded not guilty to the charges and denied the allegations. Prior to trial, the superior court, presided over by Judge Herbert B. Hoffman, ruled on the admissibility of evidence of the Santa Cruz “Trailside Murders.” It was the theory of both the People and Carpenter that a single ind