United States v. Rojas, 758 F.3d 61

Rojas was indicted for three cocaine distributions in 2011 involving undercover agent Chau who recorded meetings and calls.
Chau testified about three meetings and related phone calls; cocaine presence confirmed by tests.
Video and audio recordings were admitted for two sales; some evidence of the third sale relied on recordings and testimony.
Defense attacked Chau's credibility, gaps in recordings, and chain-of-custody issues, as well as possible lack of search of Chau's car.
Prosecutor committed two errors in closing: playing an unadmitted audio tape and making improper vouching statements in rebuttal.
District court sustained objections, gave curative instructions, and the jury was instructed to rely on properly admitted evidence

Issue	Plaintiff's Argument	Defendant's Argument	Held
Prosecutor's vouching in closing and impact	Rojas	Rojas	No reversible error; no substantial prejudice shown
Admission of unadmitted tape in closing	Rojas	Rojas	No abuse of discretion; minimal prejudice; curative instruction given

United States v. Auch, 187 F.3d 125 (1st Cir. 1999) (prosecutor improper vouching recognized)
United States v. Rodríguez-Adorno, 695 F.3d 32 (1st Cir. 2012) (improper vouching noted in recent years)
United States v. Gomes, 642 F.3d 43 (1st Cir. 2011) (repeated vouching concerns in circuit)
United States v. Mejia-Lozano, 829 F.2d 268 (1st Cir. 1987) (instruction-based relief can mitigate prejudice)
United States v. Mitchell, 596 F.3d 18 (1st Cir. 2010) (plain error standard when no trial relief requested)
United States v. Kasenge, 660 F.3d 537 (1st Cir. 2011) (plain error / relief standards)
United States v. Pagán-Ferrer, 736 F.3d 573 (1st Cir. 2013) (abuse of discretion standard for misadventure in closing)
United States v. Sepulveda, 15 F.3d 1161 (1st Cir. 1993) (curative instruction effectiveness)
Berger v. United States, 295 U.S. 78 (1935) (distinguishable misconduct for rebuke level)