Special caution is required in instances in which "[a] prosecutor flaunts the government's skills and purity of motive or where the context ... impl[ies] private knowledge of the defendant's guilt that unfortunately cannot be shared with the jury." United States v. Gomes, 642 F.3d 43, 47 (1st Cir. 2011). In this case, the appellant alleges that both the prosecutor and the court improperly vouched for the credibility of a cooperating witness (Dávila).

In addition to the evidence against Saad being overwhelming, the prosecutor's statements criticizing the witnesses' credibility were based on the inconsistency and outlandishness of their stories, making it less likely that the jury would infer that the prosecutor had "private knowledge of the defendant's guilt that unfortunately cannot be shared with the jury." United States v. Gomes, 642 F.3d 43, 47 (1st Cir. 2011). While this absence does not mean that the prosecutor's comments were appropriate, it makes it less likely that the comments were prejudicial.

Was he honest? Of course, he was.” (alteration in original)); United States v. Gomes, 642 F.3d 43, 46 (1st Cir.2011) (telling a jury that a police detective “gave you honest, candid, truthful testimony” (emphasis removed)); United States v. Castro–Davis, 612 F.3d 53, 67 (1st Cir.2010) ( “I think [the identity witness's] testimony was very clear .... It seems to me, and I submit to you, that [the witness] is right on the money.” (emphasis removed)).

We have previously noted that “the potential for harm from vouching varies, and it is likely to be more dangerous where the prosecutor flaunts the government's skills and purity of motive or where the context or the prosecutor's words imply private knowledge of the defendant's guilt that unfortunately cannot be shared with the jury.” United States v. Gomes, 642 F.3d 43, 47 (1st Cir.2011). Here, there was no such “flaunt[ing],” no implication of secret knowledge, an instruction telling the jury that statements from closing arguments are not evidence, and no other circumstances which would lead us to find that the potential for harm from the prosecutor's comments was sufficient to justify reversal on plain error review.

This case marks at least the third time in the past three years that we have noted in a published opinion improper vouching by a prosecutor. See United States v. Rodríguez–Adorno, 695 F.3d 32, 41 (1st Cir.2012); United States v. Gomes, 642 F.3d 43, 46–47 (1st Cir.2011). In this instance, the prosecutor in effect testified that he ran the investigation, and that any flaws in it were therefore not probative on the question of the witnesses' credibility.

Regarding the prosecutor's improper vouching, the First Circuit recognizes certain types of vouching as more prejudicial than others: "[I]t is likely to be more dangerous where the prosecutor flaunts the government's skills and purity of motive or where the context or the prosecutor's words imply private knowledge of the defendant's guilt that unfortunately cannot be shared with the jury." United States v. Vizcarrondo-Casanova, 763 F.3d 89, 97 (1st Cir. 2014) (quoting United States v. Gomes, 642 F.3d 43, 47 (1st Cir. 2011)). Here, the prosecutor did "flaunt[]" the agents' skills and purity of motives, id., but only briefly and in reaction to the Defendants' argument challenging the sufficiency of the investigation.