Davis v. People, 310 P.3d 58

Cameron Davis drove a car in which a passenger (“Smoke”) shot and killed a bystander; Davis admitted driving but denied prior knowledge of the shooting.
Prosecution argued Davis planned the drive-by; it relied on testimony from Davis’s girlfriend (E.W.), his mother (Ms. Monroe), and a friend (W.C.).
Detectives testified about their pretrial investigative interviews with those witnesses, describing interview tactics and stating their on-the-spot assessments (e.g., that a witness “wasn’t being forthcoming,” “hadn’t been entirely truthful,” or that another’s details were “true”).
Defense objected under Colorado Rule of Evidence (CRE) 608 as improper comments on witness credibility; the trial court overruled and sometimes gave a limiting instruction; the jury convicted Davis of lesser-included offenses.
The court of appeals affirmed, holding such testimony admissible to explain interrogation tactics and, additionally, that opening statements could open the door to otherwise inadmissible evidence; the Colorado Supreme Court granted certiorari on two questions but decided only the first.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether detectives may comment on a witness’s credibility when testifying about investigative interviews	People: Such testimony is permissible when used to explain detectives’ interrogation tactics and investigative decisions (provides necessary context).	Davis: CRE 608 bars witnesses from opining on another witness’s veracity; such testimony invades the jury’s province and is categorically improper.	Held: Admissible when offered to provide context for interrogation tactics/investigative decisions; trial court did not abuse discretion.
Whether opening statements can "open the door" to admission of otherwise inadmissible evidence	People/court of appeals (below): Opening statements may open the door to such evidence.	Davis: Opening statements are not evidence and cannot permit admission of otherwise inadmissible evidence.	Held: Court did not decide (moot) because ruling on the first issue was dispositive.

Liggett v. People, 135 P.3d 725 (Colo. 2006) (categorical prohibition on asking witnesses to opine that another witness was lying)
People v. Lopez, 129 P.3d 1061 (Colo. App. 2005) (detectives may reference witness credibility narrowly to explain interrogation techniques and context)
Kaufman v. People, 202 P.3d 542 (Colo. 2009) (trial court has broad latitude on admissibility; abuse-of-discretion standard)
People v. Gaffney, 769 P.2d 1081 (Colo. 1989) (disfavoring witness testimony that another witness’s statements were "very believable")