Commonwealth v. Denton, 75 N.E.3d 589

In December 2013 an undercover officer posing as a heroin user asked Denton for drugs; Denton obtained a bag later tested as heroin and caffeine and was arrested.
At trial Denton asserted the affirmative defense of entrapment, claiming police induced him to commit the offense.
The Commonwealth sought to rebut entrapment by introducing three prior drug convictions from 1991, 1993, and 1994 showing Denton acted as a middleman in drug deals.
Denton moved to exclude those convictions as too remote and unduly prejudicial; the judge admitted them and gave a limiting instruction that they be used only to show predisposition.
The jury convicted Denton of distribution of heroin; he appealed, arguing the admission of the aged prior convictions was erroneous. The SJC reversed and ordered a new trial.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Admissibility of prior convictions to rebut entrapment (predisposition)	Commonwealth: prior acts showing similar role (middleman) are relevant to predisposition and admissible despite age	Denton: convictions (oldest 19 years) too remote; probative value outweighed by prejudice	Reversed — convictions were too remote; probative value had diminished and admission was erroneous
Similarity requirement for propensity evidence in entrapment context	Commonwealth: facts of prior acts were sufficiently similar to charged offense	Denton: similarity insufficient to overcome remoteness and prejudice concerns	Court: some prior acts were factually similar, but similarity alone did not cure excessive remoteness
Adequacy of limiting instruction to cure potential prejudice	Commonwealth: limiting instruction suffices to mitigate prejudice	Denton: inherent danger of propensity evidence cannot be cured by instruction given age of convictions	Court: limiting instruction was insufficient to overcome the prejudice from remote convictions
Harmless error analysis	Commonwealth: any error was harmless given other evidence of culpability	Denton: error affected substantial right and requires new trial	Court: error was not harmless; new trial required

Buswell v. Commonwealth, 468 Mass. 92 (discusses use of prior bad acts to rebut entrapment)
Vargas v. Commonwealth, 417 Mass. 792 (prior-bad-acts must be sufficiently similar so probative value outweighs prejudice)
Dingle v. Commonwealth, 73 Mass. App. Ct. 274 (remote prior acts—13+ years—may be erroneously admitted)
Childs v. Commonwealth, 23 Mass. App. Ct. 33 (very old convictions can be unduly prejudicial)
Dargon v. Commonwealth, 457 Mass. 387 (standard of review for evidentiary rulings)
Crayton v. Commonwealth, 470 Mass. 228 (prior bad act evidence inadmissible if probative value outweighed by unfair prejudice)
Butler v. Commonwealth, 445 Mass. 568 (probative value of prior bad acts decreases over time)
Barrett v. Commonwealth, 418 Mass. 788 (same principle regarding diminishing probative value)
Alegata v. Commonwealth, 353 Mass. 287 (rejection of propensity-based reasoning "once a criminal always a criminal")
Whiting v. United States, 296 F.2d 512 (caution on retrospective appraisal of past conduct)