Full opinion text
KEENAN, District Judge. These five consolidated appeals arise from the convictions of the defendants, after a jury trial, for their participation in a multi-drug conspiracy. On October 4, 2002, a federal grand jury, sitting in the District of Puerto Rico, returned a two-count Indictment, charging forty-three defendants with conspiracy to distribute five kilograms or more of cocaine, fifty grams or more of crack, and one kilogram or more of heroin, in violation of 21 U.S.C. §§ 841 and 846. The charges stemmed from the defendants’ alleged participation in Las Avispas, a heroin, powder cocaine, crack, and marijuana ring that operated drug distribution centers, or drug “points,” throughout neighborhoods in the Guayama and Salinas regions of Puerto Rico, from April 1993 to September 2002. Of the forty-three defendants who were indicted, thirty-seven pleaded guilty. The present Defendants-Appellants, Mizaury López-Soto (“López-Soto”), Heriberto Ofray-Campos (“Ofray”), Pedro José Diaz-Cla-vell (“Diaz-Clavell”), Dennys Cruz-Pereira (“Cruz-Pereira”), and Modesto Zaragoza-Lasa (“Zaragoza-Lasa”) (collectively, the “Appellants”), opted to go to trial, along with an additional defendant, Carlos Esco-bar-Figueroa, whose appeal proceeded separately. Trial began on August 5, 2003 and concluded on September 29, 2003. The jury found the Appellants guilty and indicated by a special verdict form that the charged conspiracy involved the threshold amounts of the narcotics described in the Indictment. For the reasons that follow, we vacate the convictions of Diaz-Clavell and Zara-goza-Lasa and remand for new trials. We affirm the convictions of Cruz-Pereira and López-Soto but vacate their sentences and remand for re-sentencing. We affirm the conviction and sentence of Ofray. BACKGROUND In setting forth the background of this case, we present the facts in a light that is most favorable to the Government’s case and thus supportive of the jury’s verdict. We provide additional facts where they are relevant to the legal analysis of specific issues. See United States v. Rodriguez-Marrero, 390 F.3d 1, 6 (1st Cir.2004). The Government’s evidence at trial consisted, among other things, of the testimony of law enforcement agents and cooperating witnesses; audio recordings of drug transactions; and physical evidence, including guns and narcotics, recovered during the course of the investigation. The evidence established that, from 1993 to 2002, Las Avispas, a gang with approximately forty members under the leadership of José Dávila-López (a/k/a José Ca-bezón), owned and operated drug points in Guayama and Salmas from which members of the organization sold large quantities of cocaine, crack, heroin, and marijuana. The drug points operated by Las Avispas included the points at Las Vias and La Plumita, in the Borinquen ward of Guaya-ma. For several years during the time period at issue, Las Avispas was engaged in a violent war over territory in the Bor-inquen ward with a smaller gang, Los Jibaritos, that operated a drug point at Las Ruinas, in close proximity to the Las Vias and La Plumita drug points. The Las Vias point carried out a thriving narcotics trade, operating around the clock with nearly constant demand from street users. Francisco Rivera Cardona, a former Avispas street dealer who sold crack and cocaine at Las Vias from 1996 to 1999, testified that he typically sold between 400 and 500 capsules of crack per eight-hour shift, as well as approximately twenty-five $10 bags of cocaine per shift. Members of Las Avispas and Los Jibaritos regularly carried weapons and frequently engaged in shoot-outs with each other and with members of other rival gangs in the area. Las Avispas, Los Jibaritos, and other neighboring drug rings operated under similar principles. Drug point owners, such as José Cabezón, were rarely seen at the actual drug points and had limited interaction with the gangs’ lower level members. In addition to drug point owners and managers, workers in the drug rings included suppliers, who sold large quantities of narcotics on a regular basis to several different gangs; sellers, who sold the packaged drugs on the street to end users; runners, who kept the points stocked with drugs; and enforcers, who often carried firearms and used violence to protect the gangs' members, drugs, and drug proceeds from the violent encroachment of rivals. Often, members of the drug gangs occupied overlapping roles. The Government’s witnesses also described how different drugs were packaged. Cocaine and marijuana were sold in plastic bags, in $5 and $10 quantities. Crack was sold in small plastic vials, at $3 or $3.50 per vial. Heroin was packaged in aluminum foil of different colors. The heroin sold by Las Avispas at Las Vias generally was packaged in violet-colored foil. The cooperating witnesses also described how the cash proceeds were safeguarded and how the cash was spent, often on luxury items, to disguise its illicit source. Much of the testimony focused on the narcotics activity and violent conduct of members of Las Avispas who were named in the Indictment but who were not on trial. The Government also offered testimony about the seizures of drugs and firearms that were made from many of the absent co-defendants. Although the Government’s witnesses provided a comprehensive description of Las Avispas’ structure and activities, and much testimony was presented relating to the narcotics activities of the thirty-seven absent co-defendants, the quantity and quality of the proof adduced against each of the present Appellants varied markedly. The evidence offered against each Appellant was as follows. Ofray Ofray owned two bars, Rumba’s Pub and La Cota Rota, in Guayama, as well as an upholstery store in Salinas, from which he sold cocaine in “wholesale” quantities, ranging from eighths of a kilogram to full kilograms. Abdul Mendoza-Lebrón (“Mendoza-Lebrón”), a former member of Los Jibaritos who acted as second-in-command of their Las Ruinas drug point but who also sold drugs to Las Avispas in 1997 and 1998, testified that Ofray was a major cocaine supplier in Guayama. Mendoza-Lebrón purchased crack from Ofray for re-sale at Las Ruinas, usually from Ofray’s upholstery store or from Ofray’s residence in Puente Jobo, on a weekly basis from 1994 until Mendoza-Lebrón’s arrest in 1999. Mendoza-Lebrón testified that Of-ray sold large amounts of drugs to Las Avispas, Los Jibaritos and, indeed, “to anybody who would come to buy from him.” Juan Rivera-Rivera (“Rivera-Rivera”), the former leader of the rival Las Jibaritos gang during much of the time period at issue, further testified that Ofray supplied cocaine to drug points run by Las Avispas and that Rivera-Rivera personally purchased cocaine from. Ofray on one occasion, in 1997 or 1998. Carlos Collazo (“Collazo”), another cooperating witness who operated a drug point in the San Felipe ward, between Guayama and Salinas, and frequently associated with and supplied guns to Avispas members, testified that he learned from López-Soto that Ofray was a crack supplier. Angel Villodas (“Villodas”), a cooperating witness who began working as a confidential informant for the FBI in 2000, testified that, on June 8, 2001, he arranged with Ofray to purchase approximately two ounces of cocaine for $1200. Villodas made the purchase on June 14, 2001, at Rumba’s Pub. Although Villodas conferred with Ofray when he first arrived at Rumba’s Pub to complete the transaction, Villo-das testified that it was Ofray’s part-time employee, Appellant Diaz-Clavell, who delivered the cocaine to Villodas in the bathroom of Rumba’s. Villodas also testified that Ofray frequently carried an automatic weapon. In addition, law enforcement officers testified about Ofray’s possession of two handguns. Specifically, in the early morning of July 14, 2002, police officers recovered a .9mm pistol that Ofray deposited in a parked van outside of Rumba’s Pub. Later that day, while arresting Ofray, officers seized a Colt .45 pistol that Ofray carried in a duffel bag. Diaz-Clavell Diaz-Clavell had a full-time job with the Puerto Rico Department of Public Works, but also worked part-time at Ofray’s establishments, Rumba’s Pub and La Copa Rota. Mendoza-Lebrón testified that Diaz-Clavell was very frequently in Ofray’s company and often present when Mendoza-Lebrón and Ofray conducted drug deals. Mendoza-Lebrón also testified that Diaz-Clavell stashed cocaine and cash for Ofray and, on several occasions when Mendoza-Lebrón purchased cocaine from Of-ray, Diaz-Clavell brought the drugs to the apartment above Ofray’s upholstery shop, where the deals were consummated. As stated above, Villodas, who was Diaz-Clavell’s second cousin, testified that, on June 14, 2001, when Villodas went to Rumba’s Pub to execute the cocaine deal that he had pre-arranged with Ofray, it was Diaz-Clavell who delivered the two ounces of cocaine to Villodas, in the bar’s bathroom. López-Soto The Government’s cooperating witnesses, including Mendoza-Lebrón, Rivera-Rivera, and Collazo, testified at length about López-Soto’s control of several drug points, including the Olimpo point in Bor-inquen, from which López-Soto sold cocaine and crack from 1998 to 1998. Mendoza-Lebrón testified that López-Soto regularly carried weapons and acted as an enforcer for Las Avispas from 1993 through 1998, and shot one of the men working for Mendoza-Lebrón around Christmas of 1998. López-Soto conducted frequent drug deals with Las Avispas’ members at drug points in Borinquen, which remained open twenty-four hours each day. López-Soto was both a buyer and seller of narcotics; Rivera-Rivera testified that, on a particular occasion in 1996 or 1997, he sold López-Soto 100 vials of crack, and in 1998, bought one kilogram of cocaine from López-Soto. Collazo testified that he supplied automatic weapons and silencers to López-Soto in 1996 and 1997. López-Soto also was arrested in possession of a .9mm pistol in March 1998. In addition, Collazo testified that López-Soto carried out the murder of Santito, a rival drug dealer, in March 1997. Rivera-Rivera stated that López-Soto admitted to Rivera-Rivera that he had murdered San-tito. Cruz-Pereira Mendoza-Lebrón testified that Cruz-Pereira regularly purchased crack from him and his cousin, Wilson Mendoza-Vás-quez (“Wilson”) — a member of Las Avis-pas and one of the defendants named in the Indictment. Mendoza-Lebrón sold crack to Cruz-Pereira until Mendoza-Le-brón’s arrest in 1999, on those occasions when Wilson did not have crack to sell. In addition to selling crack, Mendoza-Lebrón bought “eighths” of crack from Cruz-Per-eira. The Government also presented evidence of three recorded drug purchases that were made from Cruz-Pereira. On June 21, 2001, Villodas, who had known Cruz-Pereira since their youth, went to Cruz-Pereira’s house on Santa Ana Street and arranged to purchase crack. Cruz-Pereira left in his truck and returned approximately thirty or forty minutes later with approximately fifty vials of crack, which he sold to Villodas in exchange for cash. Agent Edwin Rosa-Ferrer (“Agent Rosa-Ferrer”), an undercover officer working for the Puerto Rico Police Department, was introduced to Cruz-Pereira through an individual named “Christopher.” On November 17, 1998, Agent Rosa-Ferrer went to Cruz-Pereira’s house and arranged to purchase one gram of cocaine for $40. Agent Rosa-Ferrer later went to La Ponderosa, a bar owned by Cruz-Pereira, to complete the transaction. At La Ponderosa, Cruz-Pereira received the cocaine from Cruz-Pereira and handed the $40 to “Christopher.” On December 3, 1998, again at La Ponderosa, Agent Rosa-Ferrer purchased five grams of cocaine from Cruz-Pereira for $150. Zaragozctr-Lasa Zaragoza-Lasa, who was known by the nickname “El Viejo Mode,” was alleged to be a major heroin and cocaine supplier for Las Avispas. Cardona testified that he saw Zaragoza-Lasa, whom he knew only by the name “El Viejo Mode,” at Las Vias on “several occasions” speaking with Javier Báez, the manager of the drug point. On one occasion, in 1998, Cardona saw Zaragoza-Lasa hand to Baez a brick-shaped object wrapped in paper. Cardona testified that he believed the package contained drugs because a runner later brought to Cardona what appeared to be the package’s wrapping, and Cardona was able to make crack out of cocaine residue that was on the paper. Cardona also testified that when drug supplies at Las Vias became depleted, the stock of drugs would increase following “El Viejo Mode” ’s visit. Olga Lebrón-Ortiz (“Lebrón-Ortiz”), a cooperating witness who regularly sold marijuana and cocaine in the Borinquen ward in Guayama in 1994 and 1995 and later made undercover drug purchases for the FBI, saw Lasa — whom she also knew only by the name “El Viejo Mode” — in Borinquen regularly from 1995 through 2002. Zaragoza-Lasa appeared in Borin-quen up to twice a week. Lebrón-Ortiz stated that she saw Zaragoza-Lasa deliver to Javier Baez a transparent bag containing violet-colored aluminum foil packages. Lebrón-Ortiz corroborated other testimony that established that heroin was regularly packaged for sale by Las Avispas at Las Vias in violet-colored aluminum foil. Lebrón-Ortiz also testified that, on two occasions in 2002, she saw Zaragoza-Lasa give free samples, or “tastes,” of heroin to Borinquen street junkies. “Overview” Testimony In addition to the aforementioned testimony from cooperating witnesses and an undercover officer, the Government offered the testimony of two lead case agents, Agent Ricardo Rivera and Agent José Tirado, who were both members of the Puerto Rico Police Department assigned to the joint FBI task force investigating narcotics and weapons activity in Guayama and Salinas. Agent Rivera, the Government’s first witness, provided a general overview of the pervasive, violent drug activity in the Guayama and Salinas region, identifying eleven different drug points that were controlled by seven gangs. In addition to testifying about the general hierarchy among the workers at the drug points and the way in which drug points typically operated, Rivera-over defense counsel’s frequent objections-summarized the role played by each of the five Appellants in Las Avispas. Agent Rivera stated that Ofray dealt large quantities of drugs from his bars and upholstery shop, carried weapons regularly, and was a friend and drug supplier to José Cabezón, Las Avispas’ leader. Agent Rivera described Díaz-Clavell as Ofray’s assistant and runner, who regularly delivered drugs to Ofray. Rivera also discussed López-Soto’s role as an enforcer for Las Avispas, and his frequent carriage of weapons. Agent Rivera identified Cruz-Pereira as the leader of the Santa Ana drug point in the Puente Jobo ward. Finally, Agent Rivera stated that Zaragoza-Lasa delivered drugs regularly to Las Avispas and, in particular, supplied heroin to the Las Vias drug point. Agent Rivera did not, however, testify that he had any personal knowledge of the Appellants’ alleged narcotics activity. Rather, he derived his conclusions “through information that we obtained from informants who collaborated in the investigation and informants of the Puerto Rico Police Department and state policemen as well.” Agent Tirado provided similar “overview” testimony over defense counsel’s objections later in the trial. Like Agent Rivera, Agent Tirado explained the role each Appellant played in the Las Avispas drug organization. Agent Tirado described Ofray as a Las Avispas cocaine supplier who operated the San Felipe drug point in Salinas (that is, Ofray’s upholstery store); Díaz-Clavell as Ofray’s runner; López-Soto as a Las Avispas “hit man” and owner of a drug point; Cruz-Pereira as the manager of the Santa Ana drug point in the Puente Jobo ward; and Zara-goza-Lasa as one of Las Avispas’ suppliers, and “the main supplier of heroin at the Pales Matos drug points in the Borin-quen ward, in Guayama and other drug points” who was known to supply heroin in violet-colored aluminum foil packets. While testifying about each Appellant’s role in the conspiracy, Agent Tirado referred to a chart that contained the names and alleged positions occupied in the conspiracy by the Appellants and the other defendants named in the indictment. Like Agent Rivera, Agent Tirado conceded that his information was obtained solely through second-hand information given to him by informants and “through the investigation that we conducted.” DISCUSSION The Appellants assert numerous individual claims on appeal. One claim, which initially was raised only by Cruz-Pereira, arises from the district court’s allegedly improper handling of a jury note submitted after the close of evidence. In its written response to the note, the court imparted to the jury information that was extrinsic to the evidence presented at trial and potentially prejudicial to all five Appellants. Because the district court’s response to the jury note arguably affected the jury’s verdict as to all five Appellants, we deal first with this issue before addressing Appellants’ many individual challenges. The Jury Note On September 29, 2003, after the jury received final instructions and began deliberations, the district court told both the prosecutors and defense counsel that, if the court received a note from the jury, it would notify all counsel, and that counsel were required to arrive within ten minutes after being notified. The trial judge warned that if counsel failed to appear within ten minutes of the notification, he would respond to the jury’s note without input from anyone who was absent. The record indicates that the court subsequently received four jury notes, including the final note, which stated that the jury had reached a verdict. Two notes, the contents of which are irrelevant for purposes of this appeal, were marked as “Jury Note # 1” and “Jury Note # 3”, and were signed by the foreperson, respectively, at 5:55 p.m. and 6:00 p.m. The note which concerns us was marked as “Juror Note # 2” (“Note # 2”), and was signed by the foreperson at 6:15 p.m. Note # 2 was written in Spanish and headed with the single, underlined word “Duda,” which is translated as “Doubt.” The district court responded to the note, in English, as follows: Dear Jury: The question you posed, Those that are imprisoned, that is the others in the Indictment, are they in jail for a conspiracy? The answer is yes. s/Juan M. Pér-ez-Giménez, U.S.D.J., 9-29-03. This written answer was then sent to the jury. The final note from the jury, stating that the jury had reached a verdict, was signed by the foreperson at 7:15 p.m. As stated, Cruz-Pereira was the sole Appellant to assert a claim relating to the jury note. Cruz-Pereira claimed that the trial court’s handling of the note violated Rule 43(a) of the Federal Rules of Criminal Procedure, which requires the presence of the defendant at every stage of the trial, and that the substance of the district court’s response to the note resulted in great prejudice. The Government argued, first, that the district court’s divergence in this case from the standard practice of handling the jury note was due to defense counsel’s failure to follow the judge’s reasonable ten-minute rule; second, that the record indicated that defense counsel were in fact present when the district court drafted its proposed answer to Note #2 and did not object to the answer; and third, even if the court improperly handled the note, that the error was harmless in light of the overwhelming evidence against Cruz-Pereira. Because it is undisputed that the district court informed the jury of a fact that was never offered in evidence — namely, that thirty-seven non-testifying co-defendants were incarcerated for a conspiracy — and because that fact had the potential of tainting the jury’s verdict with respect to all of the Appellants, we exercised our discretion to review the jury note issue as it applied to all five Appellants, even though only Cruz-Pereira initially raised the claim on appeal. See United States v. Riverar-Rosario, 300 F.3d 1, 10 n. 1 (1st Cir.2002) (“In exceptional cases, especially in criminal cases, appellate courts, in the public interest, may, of their own motion, notice errors to which no exception has been taken, if the errors are obvious, or if they otherwise affect the fairness, integrity or public reputation of judicial proceedings.”) (quoting United States v. Atkinson, 297 U.S. 157, 160, 56 S.Ct. 391, 80 L.Ed. 555 (1936) (internal quotation marks omitted)). Our initial review of the procedural component of the district court’s handling of the jury note was somewhat hampered by the state of the trial transcript. As all the parties agree, the portion of the transcript that relates to the district judge’s receipt of the jury notes and his drafting of the answer to Note # 2, in particular, contains gaps and omissions. Because of the incomplete transcription, it was unclear which defense counsel, if any, were present when the judge discussed his proposed response to Note # 2. It was equally unclear whether defense counsel were given an opportunity to object to the proposed response or whether counsel in fact voiced any objections. Unsurprisingly, the briefs submitted by the Government and Appellant Cruz-Pereira contained differing interpretations of the incomplete record. Counsel’s statements at oral argument did not help to clarify the circumstances under which the district court responded to Note #2. Accordingly, we directed the parties to submit supplemental briefing on the issue of whether the district court’s handling of the jury note was erroneous, as well as affidavits from the trial attorneys, setting forth relevant facts related to the trial judge’s handling of the jury note, in an attempt to reconstruct the record. In addition, we directed the parties to address the substantive issue of prejudice that may have resulted, as to each Appellant, from the court’s answer to Note # 2. The affidavits and supplemental briefing submitted by the parties lead us to conclude that the procedure followed by the court in handling the jury note was not erroneous. In United States v. Maraj, 947 F.2d 520 (1st Cir.1991), we set forth the proper procedure for a trial court’s handling of a jury note: The preferred practice for handling a jury message should include these steps: (1) the jury’s communique should be reduced to writing; (2) the note should be marked as an exhibit for identification; (3) it should be shown, or read fully, to counsel; and (4) counsel should be given an opportunity to suggest an appropriate rejoinder. If the note requires a response ore tenus, the jury should then be recalled, the note read into the record or summarized by the court, the supplemental instructions given, and counsel afforded an opportunity to object at side-bar. If, however, the note is to be answered in writing, the court’s reply should be marked as an exhibit for identification, the judge should read both the jury’s note and the reply into the record, and counsel should be afforded an opportunity to register objections before the reply is transmitted to the jury. Id. at 525. In addition, “it is also helpful for the judge to inform counsel of the substance of [the] proposed response.... ” Id. (quoting United States v. Ronder, 639 F.2d 931, 934 (2d Cir.1981) (internal quotation marks omitted)). The rules for handling a jury note that are set forth in Maraj are well-settled. See United States v. Parent, 954 F.2d 23, 25 (1st Cir.1992) (stating that Maraj drew upon “long-settled precedent” and “stands foursquare for the proposition that messages from a deliberating jury, pertaining to ongoing deliberations, ought to be fully disclosed to the lawyers when received, so that the latter may be heard before the judge implements a course of action”). A judge’s responding to a jury note outside the presence of counsel and defendant also violates Rule 43 of the Federal Rules of Criminal Procedure, which states that the stages of a trial at which the defendant must be present include “every trial stage, including jury impanelment and the return of the verdict[.]” Fed.R.Crim.P. 43(a)(2). The affidavits submitted by the parties lead us to conclude that all parties were present at the time that the district court drafted a proposed answer to Note #2 and that the note was discussed with counsel. The affidavits received from trial counsel for López-Soto (Attorney Inserni), Zaragoza-Lasa (Attorney Cruz), and Cruz-Pereira (Attorney Dolz) all state that the attorneys do not recall whether they were present when the trial judge drafted his answer to Note # 2. The attorney who represented Ofray and Diaz-Clavell jointly at trial (Attorney Diaz) did not submit an affidavit. By contrast, the Government’s lead prosecutor at trial, Assistant United States Attorney (“AUSA”) Irene Feldman, offers a clear recollection of the events at issue. She states in her affidavit that she “quite definitely remember[s] the presence of all attorneys in the crowded room when the notes were read and the answers were discussed and drafted by the court.” In particular, AUSA Feldman states that she is “absolutely certain that the second question [Note # 2] was discussed in the presence of all parties prior to the court’s having drafted and filed a response.” In light of defense counsel’s collective uncertainty and the Government’s definitive recollection that all parties were present when the district court drafted its response to Note # 2, we find that there was no procedural error in the district court’s handling of the jury note. It is evident from the record that Note #2 was reduced to writing, and equally evident from the Government’s affidavit that the note was shown to and/or discussed with defense counsel, and that counsel thus had the opportunity to object to the proposed answer. We turn next to the issue of whether the trial judge’s response to Note #2, resulting in the jury’s exposure to potentially prejudicial extrinsic information, constituted substantive error. The Sixth Amendment requires that the jury’s verdict must be based solely upon the evidence developed at trial. See Turner v. Louisiana, 379 U.S. 466, 472, 85 S.Ct. 546, 13 L.Ed.2d 424 (1965). “The theory of our system is that the conclusions to be reached in a case will be induced only by evidence and argument in open court, and not by any outside influence, whether of private talk or public print.” Patterson v. Colorado, 205 U.S. 454, 462, 27 S.Ct. 556, 51 L.Ed. 879 (1907) (Holmes, J.). “[Exposure to extrinsic information deprives a criminal defendant of the protections of the Sixth Amendment, including his right of confrontation, of cross-examination, and of counsel.” United States v. Santana, 175 F.3d 57, 65 (1st Cir.1999) (citations and footnote omitted); see also id. (finding that “the judge should not have intervened by allowing the jury to observe [extrinsic evidence] after the close of evidence and without the standard safeguards of a criminal trial” and vacating conviction); Lacy v. Gardino, 791 F.2d 980, 983 (1st Cir.1986) (finding that defendant’s Sixth Amendment rights to confrontation and cross-examination were violated when juror peeled tape off exhibits unmasking information concerning defendant’s prior criminal record); United States v. Hans, 738 F.2d 88, 93 (3d Cir.1984) (trial court committed reversible error by granting jury’s request to examine objects not in evidence, after deliberations had begun). The jury’s exposure to extrinsic facts is especially troubling when the trial judge is the source of the information. A district court must use extreme caution in answering questions from juries so as not to usurp the jury’s fact finding role. As we have noted on many occasions “undeniably inherent in the constitutional guarantee of trial by jury is the principle that a court may not step in and direct a finding of contested fact in favor of the prosecution regardless of how overwhelmingly the evidence may point in that direction.” United States v. Sabetta, 373 F.3d 75, 80 (1st Cir.2004) (quoting United States v. Rivera-Santiago, 107 F.3d 960, 965 (1st Cir.1997)). “The Constitution casts judge and jury in mutually supporting—yet nevertheless distinct—roles.... ‘The trial judge is ... barred from attempting to override or interfere with the jurors’ independent judgment in a manner contrary to the interests of the accused.’ ” United States v. Argentine, 814 F.2d 783, 788 (1st Cir.1987) (quoting United States v. Martin Linen Supply Co., 430 U.S. 564, 573, 97 S.Ct. 1349, 51 L.Ed.2d 642 (1977)). Here, the jury requested, and the court affirmatively provided, undisputably extrinsic information. There was simply no evidence presented at trial relating to the current status of any of the thirty-seven absent co-defendants named in the Indictment. None of the thirty-seven co-defendants testified at trial, and no mention was made of whether any of the thirty-seven had been imprisoned or found guilty of the charges in the indictment. Thus, the jury’s note itself suggests that the jury had been exposed to the extrinsic “fact” that the absent co-defendants were incarcerated. More crucially, the judge’s response to Note #2, in which he confirmed for the jury that the thirty-seven co-defendants who did not appear at trial were in prison for their participation in a conspiracy, constituted new evidence, delivered to the jury from the bench rather than the witness stand, and unaccompanied by any of the safeguards of a criminal trial, in violation of Appellants’ Sixth Amendment rights. See Turner, 379 U.S. at 472-73, 85 S.Ct. 546 (“Trial by jury in a criminal case necessarily implies at the very least that the ‘evidence developed’ against a defendant shall come from the witness stand in a public courtroom where there is full judicial protection of the defendant’s right of confrontation, of cross-examination, and of counsel.”). Thus, the jury’s exposure to extrinsic information amounts to an error of constitutional dimension. Having found error, we must next select the appropriate standard for our review. Normally, in the absence of any objection to the answer that the district court proposed and submitted to the jury, we would review for plain error. The gaps in the trial transcript prevent us, however, from ascertaining whether defense counsel asserted timely objections to the court’s proposed response. The affidavits submitted in supplemental briefing do not provide much illumination. The trial attorneys for López-Soto, Zaragoza-Lasa, and Cruz-Pereira all state that, although they are unsure whether they were present when the note was discussed, they would have certainly objected if the trial judge had stated that he intended to issue a written affirmative response to Note #2. As Attorney Cruz states, “I don’t remember any type of discussion in relation to the answer to jury note number 2. I am familiar with the experience of the defense attorneys involved in this case and I believe at least one, if not all of us, would have objected to the wording contained in the answer to jury note number 2 and would have requested that the jury be advised that they were only to concern themselves with those defendants who were at trial.” AUSA Feldman’s affidavit contains only the oblique suggestion that defense counsel failed to voice objections. Regarding defense counsel’s reaction to the court’s proposed answer to Note #2, Feldman states, “I recall that defense counsel responded to the jury note and proposed response as if it were favorable to the defendants.” Feldman does not affirmatively state that she recalls that there were no objections asserted. Moreover, the Government does not claim, in its supplemental brief, that defense counsel failed to object to the district court’s proposed response. Further, Feldman’s recollection that defense counsel responded to the district court’s answer as if it were “favorable” is contradicted by the record. The transcript, though incomplete, indicates that at least one attorney raised a concern about the trial court’s answer. After the court read aloud, in English, both the question posed in Note # 2 and the answer that was given by the court, the transcript indicates that Attorney Diaz stated, “But they should know that they didn’t go to trial.” The court responded as follows: “I didn’t tell them that they didn’t go to trial. The question you posed, those that are in prison; that is the others that are in the indictment, are they in jail for conspiracy? The answer is yes.” Thus, it appears that Attorney Diaz (who, as noted, did not provide an affidavit) did go on record to express a reservation about the propriety of the court’s response. In sum, the affidavits submitted by counsel and our review of the incomplete transcript do not lead us to find that defense counsel failed to object to the trial court’s proposed response to the jury note. Rather, the record indicates that some objection was in fact asserted and thus weighs against plain error review. Ordinarily, “wherever material uncertainties result from an incomplete or indecipherable record and impede or affect our decision, we resolve such uncertainties against appellants.” Credit Francais International, S.A. v. Bio-Vita, Ltd., 78 F.3d 698, 700-01 (1st Cir.1996); see also Real v. Hogan, 828 F.2d 58, 60 (1st Cir.1987) (“[I]t is the appellant who must bear the brunt of an insufficient record on appeal.”). The rule, however, is applied typically in cases where an appellant has failed to provide an adequate record. In this instance, however, Appellants are not to blame for any ambiguities or omissions in the record. We have been provided with the necessary portions of the trial transcript. It is the transcript itself that is deficient. Mindful that “[a] criminal defendant has a right to a record on appeal which includes a complete transcript of the proceedings at trial,” United States v. Carrillo, 902 F.2d 1405, 1409 (9th Cir.1990) (citing Hardy v. United States, 375 U.S. 277, 279-82, 84 S.Ct. 424, 11 L.Ed.2d 331 (1964)), we will not resolve the transcript’s inadequacies against the Appellants. Where, as here, we deem a claim of jury contamination to be preserved, we are faced with two potential standards of review: that of abuse-of-discretion or that of harmless error. In the majority of our cases that have involved claims that a jury was improperly exposed to extrinsic information, our review has been for abuse of discretion. These cases involve the jury’s accidental exposure to potentially prejudicial material that was not offered in evidence at trial. See, e.g., United States v. Bradshaw, 281 F.3d 278 (1st Cir.2002) (un-redacted version of indictment accidentally left in jury room during deliberations); United States v. Gomes, 177 F.3d 76 (1st Cir.1999) (indictment from prior trial of defendant left in jury room); United States v. Boylan, 898 F.2d 230 (1st Cir.1990) (magazine containing potentially prejudicial article about defense counsel accidentally left in jury room). In each of these cases, the colorable claim of jury contamination was brought to light either before or after the rendering of a verdict, the trial judge conducted an inquiry to discern whether the jurors were in fact prejudiced by their exposure to outside material, and where appropriate the judge employed remedial measures, such as issuing curative instructions, see Bradshaw, 281 F.3d at 291, or dismissing potentially prejudiced jurors, see Gomes, 177 F.3d at 82. In Bradshaw, we explained that a trial court, when confronted with a claim of jury contamination, has broad discretion to “fashion an appropriate procedure for assessing whether the jury has been exposed to substantively damaging information, and if so, whether cognizable prejudice is an inevitable and ineradicable concomitant” of the jury’s exposure to improper extrinsic information. 281 F.3d at 290. Where the jury’s contact with outside information is inadvertent and not accompanied by “egregious circumstances,” and the trial judge responds to the claim of contamination by conducting an inquiry and employing remedial measures, we do not presume that the jury’s exposure to extrinsic material resulted in prejudice. Id. at 288. Instead, we review the trial judge’s actions for abuse of discretion. See United States v. Yeje-Cabrera, 430 F.3d 1, 10 (1st Cir.2005). In Bradshaw, however, we declined to hold that a presumption of prejudice could never be applied: “We leave for another day the question of whether a jury’s exposure to substantively damaging information may sometimes occur under circumstances so aggravated as to warrant the application of the ... presumption [of prejudice] even without deliberate misconduct (and if so, what those circumstances might comprise). That question simply is not presented here.” Bradshaw, 281 F.3d at 288 n. 5. Bradshaw recognized that Santana was one of those eases. In Santana, 175 F.3d at 57, we held that the jury’s exposure to outside information required the application of a presumption of prejudice. In Santana, as in this case, we confronted the “unusual” situation where the jury was exposed to extrinsic information after the close of evidence and during its deliberations, not as a result of inadvertence or juror misconduct, but rather because of the trial judge’s “approval of the jury’s request to consider information outside the record.” Id. at 65. In Santana, the trial judge permitted the jury to file back into the courtroom after the close of evidence and observe the defendant’s ears, which had remained covered throughout the trial by headphones used for the Spanish translation. A contested issue at trial was whether the defendant was in fact the individual who had participated in a drug deal that had been surveilled by a government agent; in identifying the defendant as a participant in the deal, the agent remarked on the fact that the defendant’s ears were oddly protuberant. After observing the defendant without headphones, the jury returned to its deliberations and subsequently returned a guilty verdict. There, as here, the trial judge did not conduct any inquiry into possible prejudice resulting from the jury’s exposure to extra-record evidence, nor did the court issue curative instructions or undertake any other remedial measures. Under those circumstances, we found that “the court’s decision to allow the jury to consider extrinsic information is .... subject to de novo review and it is error per se.” Id. We find that review for abuse of discretion is inappropriate in this case. Here, the jury’s exposure to extrinsic material did not occur inadvertently: the undisput-ably extrinsic information was supplied to the jury by the trial court itself, in response to the jury’s note, and thus essentially was offered to the jury as evidence. The judge, who served as the source of the extrinsic information, conducted no inquiry as to the prejudice that may have resulted from the jury’s receipt of the off-record fact and did not undertake any remedial measures. Thus, there was no action undertaken by the court that we can now review. Abuse of discretion is simply a poor fit. We conclude instead that the presumption of prejudice that we applied in Santana is also appropriate in this case. Here, as in Santana, the jury actively sought and received extrinsic information from the trial judge. Here, too, as discussed below, the information was prejudicial, was probably used by the jury as evidence of the Appellants’ guilt, and was unaccompanied by an instruction or any other curative undertaking by the district court. Accordingly, this case, like Santana, presents sufficiently aggravated circumstances that a presumption of prejudice is warranted. Because the jury’s exposure to extrinsic factual information in this case raises a presumption of prejudice, “the government bears the burden of showing beyond a reasonable doubt that the extrinsic information did not contribute to the conviction.” Id. at 66 (citations omitted); see also Lacy, 791 F.2d at 983. An error will be deemed harmless if “the beneficiary of ... [the] constitutional error [can] prove beyond a reasonable doubt that the error complained of did not contribute to the verdict obtained.” Chapman v. California, 386 U.S. 18, 24, 87 S.Ct. 824, 17 L.Ed.2d 705 (1967); see also Santana, 175 F.3d at 66. In Sullivan v. Louisiana, 508 U.S. 275, 113 S.Ct. 2078, 124 L.Ed.2d 182 (1993), the Supreme Court explained that the harmless error inquiry is “not whether, in a trial that occurred without the error, a guilty verdict surely would have been rendered, but whether the guilty verdict actually rendered in this trial was surely unattributable to the error.” Id. at 279, 113 S.Ct. 2078. To determine whether the jury’s exposure to extrinsic evidence was harmless, a reviewing court must “assess the record as a whole to determine the impact of the improper evidence upon the jury-The prejudicial effect of the improper evidence must be weighed against the weight of the properly admitted evidence.” Lacy, 791 F.2d at 986 (quoting Morgan v. Hall, 569 F.2d 1161, 1166 (1st Cir.1978) (internal quotation marks omitted)); see also United States v. Weiss, 752 F.2d 777, 783 (2d Cir.1985) (possibility of prejudice is assessed “by reviewing the entire record, analyzing the substance of the extrinsic evidence, and comparing it to that information of which the jurors were properly aware”). The inquiry regarding harmless error analysis “is case-specific” and requires consideration, among other factors, of “the centrality of the tainted evidence, its uniqueness, its prejudicial impact, the use to which the evidence was put, and the relative strength of the parties’ cases.” United States v. Garcia-Morales, 382 F.3d 12, 17 (1st Cir.2004). We first examine “the nature of the extrinsic information to which the jury was exposed to determine its potential prejudicial effect.” Santana, 175 F.3d at 66. Second, we analyze the weight of the trial evidence properly adduced against each of the five Appellants. See id. Nature of the Prejudicial Information Both the information conveyed to the jury and the manner of its conveyance were prejudicial. The district court’s confirmation that the thirty-seven defendants named in the Indictment who did not appear at trial were all incarcerated for participation in the conspiracy was tantamount to an announcement to the jury that the thirty-seven absent defendants had been convicted of the charges contained in the Indictment. The Government concedes, as it must, that “[t]he fact that other co-defendants are in prison for the same conspiracy” is “irrelevant to the guilt of those on trial.” Courts in this and other circuits have strongly cautioned against the admission of such evidence. “[A] defendant is entitled to have the question of his guilt determined upon the evidence against him, not on whether a codefendant or government witness has been convicted of the same charge.” United States v. Dworken, 855 F.2d 12, 30 (1st Cir.1988) (quoting United States v. Miranda, 593 F.2d 590, 594 (5th Cir.1979) (internal quotation marks omitted)). The potential for prejudice is present where evidence of a co-conspirator’s conviction is admitted for substantive purposes. See United States v. Blevins, 960 F.2d 1252, 1260-62 (4th Cir.1992). Under such circumstances, the jury may abdicate its duty and “regard the issue of the remaining defendant’s guilt as settled and the trial as a mere formality.” United States v. Griffin, 778 F.2d 707, 711 (11th Cir.1985). As the Fifth Circuit, reversing a conviction on the grounds that the jury was told that a non-testifying co-defendant had pleaded guilty, explained in United States v. Hansen, 544 F.2d 778 (5th Cir.1977): “There is no need to advise the jury or its prospective members that some one not in court, not on trial, and not to be tried, has pleaded guilty. The prejudice to the remaining parties who are charged with complicity in the acts of the self-confessed guilty participant is obvious.” Id. at 780. Regardless of whether an absent co-defendant has pleaded guilty or been convicted after trial, the admission of such evidence not only results in the danger that the jury will improperly infer guilt by association, it also “significantly undercuts the defendant’s right to have a jury’s verdict based only upon evidence that is presented in open court and is thereby subject to scrutiny by the defendant.” Blevins, 960 F.2d at 1260. Thus, “where a missing co-defendant does not testify, ‘it is generally accepted that absent agreement, courts and prosecutors generally are forbidden from mentioning that a co-defendant has either pled guilty or been convicted.’ ” United States v. Carraway, 108 F.3d 745, 756 (7th Cir.1997) (quoting United States v. Johnson, 26 F.3d 669, 677 (7th Cir.1994) (internal quotation marks omitted)). Where, as here, the defendants are being tried for their participation in an alleged conspiracy that took place over the course of nearly a decade, the danger that the defendants will be found guilty by sheer association with guilty non-testifying co-defendants is great. See United States v. Izzi 613 F.2d 1205, 1210 (1st Cir.1980) (“Guilt by association is one of the ever present dangers in a conspiracy count that covers an extended period.”) (citing Kotteakos v. United States, 328 U.S. 750, 774-75, 66 S.Ct. 1239, 90 L.Ed. 1557 (1946)). Justice Jackson, in his well-known concurrence in Krulewitch v. United States, 336 U.S. 440, 69 S.Ct. 716, 93 L.Ed. 790 (1949), reflected on the abnormally high risk to co-defendants in a conspiracy trial of being found guilty by association: A co-defendant in a conspiracy trial occupies an uneasy seat. There generally will be evidence of wrongdoing by somebody. It is difficult for the individual to make his own case stand on its own merits in the minds of jurors who are ready to believe that birds of a feather are flocked together. Id. at 454, 69 S.Ct. 716 (Jackson, J., concurring). Although a jury “may wonder what happened to the co-defendants whose names have been mentioned in the indictment and in the course of the trial but who have not appeared before them,” the preferred course is simply to instruct the jury “not to concern itself with that question.” Carraway, 108 F.3d at 756; see also Edward J. Devitt, Charles B. Blackmar, et al., Federal Jury Practice and Instructions § 5.02, at 106 (1992). The district court’s announcement to the jury that thirty-seven absent co-defendants named in the Indictment were incarcerated for the charged conspiracy increased by an order of magnitude the risk that the Appellants would be found guilty because of their association with the absent alleged co-conspirators, rather than because of the evidence offered at trial. Quite simply, the extrinsic information allowed the jury to draw the prejudicial inference that, if thirty-seven non-testifying co-defendants had been found guilty of the crimes described in the Indictment, the Appellants also must be guilty. Moreover, the court did not instruct the jury that the incarcerated status of the thirty-seven absent co-defendants, or the fact that they may have been found guilty, should have no bearing on the jury’s verdict with respect to each of the defendants on trial. See United States v. Riverar-Santiago, 872 F.2d 1073, 1083 (1st Cir. 1989). Absent the safeguard of a proper instruction, the prejudice arising from the court’s response to the note is even more serious. The Government claims that the district court’s answer was not especially prejudicial because “the jury note itself illustrates the jury already had knowledge that the other co-defendants were imprisoned, as it begins with the phrase, ‘those that are imprisoned.’ ” The Government’s argument is unavailing. To the extent that the note reveals that the jury knew that the absent co-defendants were imprisoned, as discussed above, such awareness was not gleaned from evidence presented at trial. The fact that the jury demonstrated its knowledge of an undisputably extrinsic fact does not cut against our evaluation of the prejudicial impact of the jury note and the district court’s response. As stated, the Sixth Amendment requires that a jury’s verdict must be based solely upon the evidence developed at trial, see Turner, 379 U.S. at 472, 85 S.Ct. 546, and “[t]he jury’s exposure during its deliberations to extrinsic information, whatever its source, is an error of constitutional proportions .... ” Santana, 175 F.3d at 65 (emphasis added). Moreover, the Government cannot, and does not, attempt to deny that the most prejudicial extrinsic information in fact came from the trial judge — namely, confirmation that the thirty-seven alleged co-conspirators were imprisoned for the conspiracy. It was this information that most readily permitted the jury to draw the impermissible inference of guilt by association. We also find that the manner in which the jury requested the extrinsic information suggests that a direct connection existed between the extrinsic evidence and the jury’s verdict. The fact that the note was headed by the word “Duda,” or “Doubt,” strongly indicates that the jury may have sustained doubt about some or all of the Appellants’ involvement in the charged conspiracy and was looking to the trial judge to resolve that doubt. See Rivera-Santiago, 107 F.3d at 966 (finding it “significant,” in determining that district court had exposed jury to extrinsic information, that jury was asking for judge to provide portion of record to “ ‘clarify some doubts’ ”). That the jury actively sought the information that it received, rather than obtained it accidentally or in an otherwise unsolicited fashion, further indicates that the answer was important to its verdict. See Santana, 175 F.3d at 67 (“[B]eeause the jurors specifically asked to observe Santana without his headphones, they obviously deemed such evidence important to their deliberations.”). It is also important, in considering prejudice, that the answer to the jury’s question was supplied by the trial judge, and thus stamped with the imprimatur of the court, rather than by comparatively less authoritative sources, such as prosecutorial comment, juror misconduct, or the inadvertent admission of extrinsic evidence into the jury room. See id.; Argentine, 814 F.2d at 788. Finally, the fact that the jury returned with a verdict a mere forty-five minutes after receiving the answer to Note # 2, which was the last note the jury sent out prior to the announcement that it had reached a verdict, supports the inference that the jury attributed weight to the trial judge’s response, and indeed considered the court’s response to be important, if not critical, in arriving at the verdict. See Rogers v. United States, 422 U.S. 35, 40, 95 S.Ct. 2091, 45 L.Ed.2d 1 (1975) (noting that jury’s returning with a verdict “five minutes” after receiving judge’s response to query weighed in favor of finding that judicial response to note was harmful error); Rivera-Santiago, 107 F.3d at 967 (drawing inference that judge’s improper response to jury influenced verdict where jury returned verdict two hours after receiving judge’s answer and noting that timing of jury’s response to judge’s answer was factor to consider in harmless error analysis). Thus, although the “fact” of the absent co-defendants’ incarceration was neither raised nor disputed at trial, and although it was not proper for the jury to consider such a fact in reaching a verdict, it was clearly information that was material to the jury’s verdict. See Santana, 175 F.3d at 67 (finding that “the connection between the extrinsic information at issue here—the appearance of Santana’s ears—and an issue material to and disputed throughout the trial—the identity of the [supplier of] crack cocaine—is unmistakable”). In sum, the nature of the extrinsic information received by the jury was prejudicial to the Appellants. Weight of the Evidence Because the relative strength of the Government’s case varied as to each Appellant, we consider each of the Appellants in turn, in light of the court’s response to Note # 2. López-Soto The error was harmless as to Ló-pez-Soto. The evidence clearly established that López-Soto was a member of the Avispas conspiracy and, more particularly, an enforcer for the organization who regularly carried guns and engaged in violence. Juan Rivera-Rivera, who lived near López-Soto in Marín and frequently associated with members of Las Avispas before the Avispas and Los Jibaritos became embroiled in a war over territory, provided ample, detailed testimony about López-Soto’s ownership of drug points at Olimpo, Las Palmas de Arroyo, Marin, and El Flamboyan. The evidence showed that López-Soto sold crack and cocaine from Olimpo from 1993 through 1998. Rivera-Rivera testified about specific drug deals in which he engaged with López-Soto, including the sale of 100 vials of crack to López-Soto in 1996 or 1997 and the purchase from López-Soto of one kilogram of cocaine in 1998. Rivera-Rivera identified specific individuals who assisted López-Soto in drug dealing, including Freddie El Agente and “Cabe,” in Olimpo. Further testimony established that Ló-pez-Soto acted as an enforcer for Las Avispas who regularly carried and used guns. Testimony was presented about Ló-pez-Soto’s participation in specific acts of violence, including his participation in an attempted contract “hit” of a rival drug dealer, with Rivera-Rivera, and his murder of rival dealer Santito in 1997. Collazo also provided detailed testimony about Ló-pez-Soto’s narcotics activity, including his purchase of large quantities of cocaine which López-Soto subsequently cooked into crack. In addition, Collazo testified about specific weapons, including automatic weapons equipped with silencers, that he sold to Zaragoza-Lasa, thus supporting the Government’s theory that López-Soto acted as an enforcer for Las Avispas. In light of the Government’s strong evidence of López-Soto’s participation in the charged conspiracy, and the comparative weakness of the defense’s case, we conclude that the guilty verdict was “surely unattributable” to the district court’s answer to the jury note. Sullivan, 508 U.S. at 279,113 S.Ct. 2078. Ofray The Government’s case against Ofray was overwhelming. Mendoza-Le-brón testified at length that Ofray supplied large-unit quantities of cocaine to Las Av-ispas on a weekly basis from 1994 through 1999. There was ample testimony establishing that Ofray frequently sold narcotics from his businesses in Salinas and Guaya-ma, which included an upholstery store, Rumba’s Pub, and La Copa Rota. Mendoza-Lebrón testified that he frequently contacted Ofray by cellular phone to arrange purchases and designate a meeting place, and that Ofray would subsequently meet Mendoza-Lebrón at the designated place and there receive drugs from Ofray in exchange for cash. Rivera-Rivera also testified about Ofray’s sale of cocaine to Las Avispas and his purchase from Ofray of nearly one kilogram of cocaine in 1997 or 1998. In addition, Villodas testified in detail about the purchase of cocaine that he prearranged with Ofray on June 8, 2001, in which he agreed to buy two ounces of cocaine for $1200. Villodas provided further testimony about the execution of the sale on June 14, 2001, in which Villodas— while wearing a monitoring device — went to La Copa Rota, as arranged, met with Ofray, and shortly thereafter received the cocaine. Finally, law enforcement testimony established that a ,9mm pistol belonging to Ofray was recovered from outside Rumba’s Pub and a Colt .45 pistol was seized from Ofray’s duffle bag at the time of his arrest on July 14, 2002. As with López-Soto, the strength of the government’s case leads us to conclude that the extrinsic information to which the jury was exposed did not sway the verdict as to López-Soto and was thus harmless beyond a reasonable doubt. Cruz-Pereira The district court’s error also was harmless beyond a reasonable doubt as to Cruz-Pereira. There was convincing evidence of Cruz-Pereira’s participation in three pre-arranged drug buys. Agent Rosa-Ferrer purchased cocaine on two separate occasions from Cruz-Pereira, on November 17, 1998 and December 3, 1998, at Cruz-Pereira’s bar, La Ponderosa. Angel Villodas, wearing a monitoring device, purchased vials of crack from Cruz-Per-eira on June 21, 2001, in the backyard of Cruz-Pereira’s residence in Santa Ana. Mendoza-Lebrón also testified that Cruz-Pereira purchased crack from Mendoza-Lebrón’s cousin, Wilson — a member of Las Avispas — and from Mendoza-Le-brón himself in large quantities and on -a weekly basis until Mendoza-Lebrón’s arrest in 1999. Mendoza-Lebrón also stated that he purchased crack from Cruz-Per-eira. Because the evidence of Cruz-Pereira’s drug dealing was strong, if not overwhelming, and was supported by additional evidence to show that Cruz-Pereira engaged in narcotics activity with non-government actors, including Mendoza-Lebrón and Wilson, we find that the district court’s erroneous answer to the jury note was harmless beyond a reasonable doubt as to Cruz-Pereira. Diaz-Clavell By contrast, the evidence presented against Diaz-Clavell, while legally sufficient to support his conviction for participation in the conspiracy, was not strong enough to persuade us beyond any reasonable doubt that the jury’s verdict of guilt was surely unattributable to the court’s response to Note # 2. See Santana, 175 F.3d at 67. The case against Diaz-Clavell relied exclusively on the testimony of cooperating witnesses. See United States v. Bosch, 584 F.2d 1113, 1123 (1st Cir.1978) (finding government’s case “not overwhelming” and constitutional error harmful, in part, because “[t]he government’s case consisted primarily of the testimony of admitted accomplices, whose credibility was attacked”). Although it was undisputed that Diaz-Clavell worked as a part-time employee at Ofray’s businesses, and the Government presented substantial evidence to establish that Ofray was a major cocaine supplier to Avispas, proof of Diaz-Clavell’s narcotics activity was relatively scant. Inculpating testimony was limited to the testimony of Mendoza-Lebrón, who stated that Diaz-Clavell assisted Ofray in his drug dealing by stashing cocaine and cash; and the testimony of Villodas, who testified that Diaz-Clavell delivered approximately two ounces of cocaine to Villo-das on one occasion, on June 14, 2001, in the bathroom of La Copa Rota, after Villo-das had arranged several days earlier to buy cocaine from Ofray. Mendoza-Lebrón initially stated only that he often saw Diaz-Clavell present during drug deals that Ofray conducted and that “whenever Eric [Ofray] gave things to me, Pepe [Diaz-Clavell] would always be present....” When asked whether Diaz-Clavell did “anything in relation to the drug deal?”, Mendoza-Lebrón answered as follows, “Well, most of the time. I can’t say all of the time because not all of the time was he [Diaz-Clavell] with Eric but he was present during several transactions that I did with Eric.” It is well-settled that such testimony, establishing nothing beyond the fact that Diaz-Clavell was present during drug transactions, without more, would not make him culpable of conspiracy. See, e.g., United States v. Guerrero, 114 F.3d 332, 342 (1st Cir.1997) (“[P]roof of sufficient participation in the crime, as well as knowledge of it, is required to convict; the defendant’s ‘mere presence’ at the scene of criminal activity is not enough.”); United States v. Ocampo, 964 F.2d 80, 82 (1st Cir.1992) (although defendant knew that her residence was used by co-defendant for drug dealing, government must also prove defendant’s participation); United States v. Hyson, 721 F.2d 856, 862-63 (1s