Commonwealth v. Lopez, AC 15-P-1183

Defendant (age 55) was convicted of multiple sex offenses based solely on the testimony of a then‑15‑year‑old who described an assault when she was 12. No physical or independent corroborating evidence was presented.
The child had documented cognitive delays, special education needs, bipolar disorder, and a prior childhood rape by an older cousin; she received ongoing therapeutic mentoring from Jill Larson.
The Commonwealth obtained permission to call Larson as the first‑complaint witness instead of the child’s father and presented Larson’s testimony about the mentor relationship and the child’s disclosure of the alleged assault.
Larson also described the child’s difficulty with imaginative or “pretend princess” play and said the child struggled with higher‑order thinking; defense objections were sustained in part but some testimony about the Plaster Fun Time incident was admitted.
In closing, the prosecutor used Larson’s testimony to argue the child lacked the sophistication to fabricate the accusation; defense argued the child confused memories of an earlier assault with the alleged incident.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Admissibility of testimony about the child’s inability to engage in imaginative play	Testimony provided contextual background about the child’s functioning and relationship with her mentor	Testimony was irrelevant to what happened and exceeded proper background; it invaded the province of the jury on credibility	Testimony about inability to engage in imaginative play was not sufficiently probative of the events and was improperly admitted for an improper purpose
Whether Larson’s testimony impermissibly vouched for the child’s credibility	Testimony merely described observations of the child’s functioning, not an opinion about veracity	Testimony implicitly vouched for the child by suggesting she could not fabricate or fantasize	Court held the testimony functioned as implicit vouching and therefore violated the bar on witness opinion about another witness’s credibility
Prejudice and need for new trial	Admission was harmless because jury could assess credibility given other evidence	Because the victim’s credibility was the sole issue and Larson had the veneer of expertise, the improper testimony likely influenced the jury	Error was prejudicial under Flebotte; convictions reversed and verdicts set aside

Commonwealth v. King, 445 Mass. 217 (allowing first‑complaint witness in certain circumstances)
Commonwealth v. Quinn, 469 Mass. 641 (witnesses may not give opinions on another witness’s credibility)
Commonwealth v. Montanino, 409 Mass. 500 (longstanding rule barring witness opinions on credibility)
Commonwealth v. Ianello, 401 Mass. 197 (impermissible testimony that effectively vouches for victim’s credibility)
Commonwealth v. LaCaprucia, 41 Mass. App. Ct. 496 (treating witness can acquire veneer of expertise and risk implicit vouching)
Commonwealth v. Flebotte, 417 Mass. 348 (standard for prejudicial error when objections were timely and forceful)
Commonwealth v. Ruffen, 399 Mass. 811 (Ruffen defense: prior similar abuse relevant to victim’s knowledge of sexual matters)