Peo v. Marler

CourtColorado Court of Appeals
DecidedMay 14, 2026
Docket23CA1128
StatusUnpublished

This text of Peo v. Marler (Peo v. Marler) is published on Counsel Stack Legal Research, covering Colorado Court of Appeals primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Peo v. Marler, (Colo. Ct. App. 2026).

Opinion

23CA1128 Peo v Marler 05-14-2026

COLORADO COURT OF APPEALS

Court of Appeals No. 23CA1128 Boulder County District Court No. 22CR455 Honorable Nancy W. Salomone, Judge

The People of the State of Colorado,

Plaintiff-Appellee,

v.

Collin Sonny Kalel Marler,

Defendant-Appellant.

JUDGMENT AFFIRMED

Division I Opinion by JUDGE J. JONES Lum and Meirink, JJ., concur

NOT PUBLISHED PURSUANT TO C.A.R. 35(e) Announced May 14, 2026

Philip J. Weiser, Attorney General, Brittany Limes Zehner, Senior Assistant Attorney General and Assistant Solicitor General, Denver, Colorado, for Plaintiff-Appellee

Megan A. Ring, Colorado State Public Defender, River B. Sedaka, Deputy State Public Defender, Denver, Colorado, for Defendant-Appellant ¶1 Defendant, Collin Sonny Kalel Marler, appeals the district

court’s judgment of conviction entered on jury verdicts finding him

guilty of first degree murder (after deliberation) and menacing. He

also appeals his sentence of life in prison without the possibility of

parole (LWOP). We affirm.

I. Background

¶2 After moving out of his father’s house, twenty-year-old Marler

moved into a condo with his cousin (T.S.), his aunt (T.S.’s mother),

and his grandmother. Marler brought his computer and kept it in

T.S.’s room, where they often played computer games together.

¶3 Marler had been living at the condo only a week when he and

T.S. got into a heated argument about T.S.’s room being messy.

The argument ended that night when Marler moved his computer

out of T.S.’s room and slept in the basement.

¶4 The next day, Marler heard his grandmother, his aunt, and

T.S. discussing the previous night’s argument. He accused them of

talking about him behind his back, and he and T.S. started to

argue. Marler’s grandmother and aunt stepped in to stop the

argument. Marler’s grandmother, his aunt, and T.S. decided to go

grocery shopping to put some distance between T.S. and Marler.

1 When they returned, Marler was in the first-floor bathroom, with

the door shut. Marler’s aunt and T.S. went to the basement,

leaving Marler’s grandmother in the living room. Marler stayed in

the bathroom for at least thirty minutes.

¶5 Marler then came out of the bathroom holding a rifle. He went

into the living room and removed the magazine from the rifle. His

grandmother took the magazine from him and put it under her arm.

Marler put the rifle on the couch and covered it with a blanket.

Marler asked his grandmother, “[D]o you know why I’ve been in the

bathroom?” His grandmother said she didn’t, and Marler

responded, “I’ve been trying to talk myself out of killing [T.S.].”

Marler’s grandmother told Marler that he wasn’t going to kill T.S.,

and he replied, “Yes, I am. I am gonna kill him.”

¶6 Marler and his grandmother talked for a few minutes about

his intent to kill T.S. Several times, Marler told his grandmother he

was going to kill T.S. Marler also kept trying to grab the magazine

from his grandmother, and she eventually let him take it.

¶7 Marler’s grandmother then told Marler, “If you and [T.S.] can’t

get this straightened out and come to an agreement, . . . you’re

going to have to go back to your dad’s.” Marler picked up the rifle

2 from the couch and said, “I’m gonna kill him.” Marler’s

grandmother said, “Then I’m gonna call the cops,” and Marler said,

“You should call the cops. Go ahead.” He then went into the

basement and immediately shot T.S. numerous times, including

once in the back after T.S. fell. Marler came back up from the

basement, threw down the rifle, and ran out the front door. T.S.

was taken to the hospital where he was later pronounced dead.

¶8 Shortly after Marler left the condo, officers pulled him over and

found the rifle magazine in his pocket. Marler was arrested and

charged with first degree murder (after deliberation) and menacing.

A jury found him guilty on both charges. The district court

sentenced him to LWOP in the custody of the Colorado Department

of Corrections.

II. Discussion

¶9 With respect to the verdicts, Marler contends that the district

court (1) abused its discretion by excluding his expert witnesses

and (2) erroneously denied his attorney’s challenges for cause to

three prospective jurors. With respect to sentencing, he contends

that (1) his sentence of LWOP is unconstitutional, and (2) the court

erred by imposing restitution. We reject each of his contentions.

3 A. Marler’s Expert Witnesses

¶ 10 Marler initially contends that the district court abused its

discretion by excluding his proffered brain development expert

witnesses because youthfulness isn’t a mental condition requiring a

court-ordered examination, and the experts weren’t going to discuss

his mental condition. We conclude that any error was harmless.

1. Additional Facts

¶ 11 Marler’s attorney endorsed two expert witnesses to testify

about brain development in adolescents. Specifically, they were

going to opine that “maturation of the prefrontal cortex is not fully

complete until the mid to late twenties, with some speculating for

men even into the early thirties” and that those without a fully

formed prefrontal cortex tend to act more impulsively.

¶ 12 The prosecution moved to strike the experts. It argued that

this was “an attempt to introduce expert testimony related to a

mental condition” and that such testimony wasn’t admissible

unless Marler underwent a court-ordered examination as required

by section 16-8-107(3)(b), C.R.S. 2025. Marler’s counsel argued

that section 16-8-107(3)(b) didn’t apply because youthfulness isn’t a

mental condition and that the experts weren’t going to discuss

4 Marler’s mental condition specifically. Rather, counsel said, the

testimony was being offered only to show the effect brain

development “could have on the ability of an adolescent to form

necessary culpable mental states.” The court disallowed the

testimony, ruling that it was subject to section 16-8-107(3)(b), with

which Marler’s counsel hadn’t complied.

2. Standard of Review

¶ 13 “We review a trial court’s determination regarding the

admissibility of evidence for an abuse of discretion.” People v. Lane,

2014 COA 48, ¶ 21 (considering a ruling denying expert testimony

regarding the defendant’s mental state). “A court abuses its

discretion if its decision is manifestly arbitrary, unreasonable, or

unfair, or if it misapplies the law.” People v. Ray, 2025 CO 42M,

¶ 19.

5 ¶ 14 We review preserved evidentiary errors for harmless error. Id.

at ¶ 20.1 “An error is harmless if it doesn’t substantially influence

the jury’s verdict or affect the fairness of the trial proceedings.” Id.

3. Analysis

¶ 15 Under section 16-8-107(3)(b), a defendant can’t introduce

expert opinion of his mental condition without first undergoing a

court-ordered examination. The term “mental condition” isn’t

defined by the statute. People v. Flippo, 159 P.3d 100, 102 (Colo.

2007). But the term has been broadly construed to include

learning disorders, People v. Wilburn, 2012 CO 21, ¶ 28; intellectual

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Peo v. Marler, Counsel Stack Legal Research, https://law.counselstack.com/opinion/peo-v-marler-coloctapp-2026.