v. Williams, 2020 CO 78

Defendant Barnett Williams was convicted of class-three felony distribution of a schedule II controlled substance after a controlled buy in which a paid informant returned with a wrapped rock later tested as cocaine; police testified to strip searches and use of a listening device, and a later apartment search recovered a scale.
At trial the prosecution introduced, under CRE 404(b), evidence of a separate prior controlled buy several months earlier (different informant) for which Williams had pled guilty to selling cocaine; that buy occurred at a different apartment within about a mile.
Defense attacked informant credibility and identity of the apartment resident but presented no witnesses or affirmative theory-of-the-case instruction.
The court of appeals reversed the conviction, holding the 404(b) evidence was improperly admitted for modus operandi and common-plan purposes; the People petitioned for review.
The Colorado Supreme Court affirmed the court of appeals for different reasons: the trial court failed to articulate a precise evidential hypothesis and, applying the Spoto/Garner four-part/CRE 403 framework, the incremental probative value of the prior-sale evidence was substantially outweighed by unfair prejudice; the error was not harmless.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether 404(b) modus operandi evidence is limited to proving identity	People: modus operandi/common-scheme evidence admissible to show pattern making identity more likely	Williams: prior sale irrelevant, highly prejudicial, not probative of identity	Court: not so limited conceptually, but here prosecution failed to articulate a precise evidential hypothesis and the evidence’s marginal probative value was substantially outweighed by prejudice
Whether common plan/scheme evidence requires a preexisting plan that included the charged crime	People: common-plan doctrine can support admissibility where facts show similar plan or method	Williams: no showing of preexisting plan linking prior sale to charged sale	Court: common-plan need not fit pre-Rules formulas, but here facts did not show sufficient similarity/frequency/uniqueness to support admissibility
Whether erroneous admission was harmless	People: other evidence (informant, police corroboration, chemist) made error harmless	Williams: prior-act evidence likely affected juror assessment of credibility and guilt	Court: error was not harmless — reasonable probability admission affected outcome

Stull v. People, 344 P.2d 455 (Colo. 1959) (early rule requiring out-of-jury proffers and limiting jury use of other-crime evidence)
People v. Spoto, 795 P.2d 1314 (Colo. 1990) (articulated four-part analysis for other-crime evidence relevancy)
People v. Garner, 806 P.2d 366 (Colo. 1991) (refined Spoto framework; explained CRE 404(b) purposes)
People v. Rath, 44 P.3d 1033 (Colo. 2002) (applied Spoto/Garner and emphasized incremental probative-value balancing)
People v. Honey, 596 P.2d 751 (Colo. 1979) (pre-Rules necessity concept contrasted with Rules approach)
People v. Jones, 311 P.3d 274 (Colo. 2013) (discussed interplay of statute and Rules for sexual-offense evidence)
Yusem v. People, 210 P.3d 458 (Colo. 2009) (harmless-error standard: no reasonable probability of a different outcome)
People v. Garcia, 28 P.3d 340 (Colo. 2001) (harmless-error principles)
Martin v. People, 738 P.2d 789 (Colo. 1987) (incremental probative value concept under Rule 403)