Peo v. Marler

Colorado Court of Appeals·Decided May 14, 2026·No. 23CA1128·Unpublished

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.

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

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.

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

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.

¶ 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

1 Marler argues that we should review the error under the

constitutional harmless error standard because it affected his constitutional right to present a defense. But “[a]n evidentiary error precluding a defendant from presenting evidence may be of constitutional magnitude ‘only where the defendant was denied virtually his [or her] only means of effectively testing significant prosecution evidence.’” People v. Shanks, 2019 COA 160, ¶ 67 (quoting People v. Brown, 2014 COA 155M-2, ¶ 6). Marler wasn’t deprived of his only way of attacking the prosecution’s theory when the court excluded his expert witnesses; thus, the constitutional harmless standard doesn’t apply. Nonetheless, even if we were to apply that standard, we would conclude that any error was harmless beyond a reasonable doubt. See Bartley v. People, 817 P.2d 1029, 1034 (Colo. 1991) (constitutional error in admitting evidence was harmless beyond a reasonable doubt when the properly admitted evidence overwhelmingly proved the defendant’s guilt).

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