People v. Kubuugu, 433 P.3d 1214

Deputy Luton observed Simon Kubuugu drive erratically with his seven‑year‑old child in the car, park, try to leave, and then exit holding a beer can; empty beer cans were later found in the vehicle.
No breath, blood, or field sobriety tests were administered; Kubuugu testified he only took a few sips after parking and that the empty cans were from another day.
At trial, without being qualified as an expert, Deputy Luton testified as a lay witness that Kubuugu smelled of alcohol and, relying on his training and experience (including “wet lab” training), that the odor was a “metabolized” alcohol smell indicating consumption prior to parking and consistent with the number of empty cans found.
Defense objected that those portions of the officer’s testimony were expert opinion disguised as lay testimony; the trial court overruled the objections and the jury convicted Kubuugu of several offenses including driving while ability impaired and child abuse.
The court of appeals held the officer’s metabolized‑alcohol testimony was improperly admitted expert testimony and that the error was not harmless; the Colorado Supreme Court granted certiorari and affirmed the court of appeals.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether testimony about detecting “metabolized” alcohol and inferring volume/timing is lay or expert opinion	Officer’s observations were perception‑based and thus admissible as lay testimony under CRE 701	Testimony rested on specialized training/experience and so was expert opinion under CRE 702 requiring qualification	Testimony was expert opinion and admission without qualification was an abuse of discretion
Whether the admission of the officer’s metabolized‑alcohol opinion was harmless error	The other evidence (erratic driving, beer can in hand, empty cans, smell of alcohol) supported the verdict so any error was harmless	The metabolized‑alcohol opinion was the only evidence directly refuting Kubuugu’s claim he drank only after parking, so error was prejudicial	Error was not harmless; it substantially influenced the verdict

Venalonzo v. People, 388 P.3d 868 (Colo. 2017) (distinguishes lay vs. expert opinion by the nature of the experience required to form the opinion)
People v. Stewart, 55 P.3d 107 (Colo. 2002) (standard of review for evidentiary rulings: abuse of discretion)
Romero v. People, 393 P.3d 973 (Colo. 2017) (harmless‑error review for preserved nonconstitutional errors)
Tevlin v. People, 715 P.2d 338 (Colo. 1986) (error is reversible when it substantially influences the verdict)