Peo v. Nielsen

CourtColorado Court of Appeals
DecidedAugust 7, 2025
Docket22CA1352
StatusUnpublished

This text of Peo v. Nielsen (Peo v. Nielsen) 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. Nielsen, (Colo. Ct. App. 2025).

Opinion

22CA1352 Peo v Nielsen 08-07-2025

COLORADO COURT OF APPEALS

Court of Appeals No. 22CA1352 Fremont County District Court No. 20CR524 Honorable Ronald M. Mullins, Judge

The People of the State of Colorado,

Plaintiff-Appellee,

v.

Mark Nielsen,

Defendant-Appellant.

JUDGMENT AFFIRMED

Division VII Opinion by JUDGE LIPINSKY Pawar and Lum, JJ., concur

NOT PUBLISHED PURSUANT TO C.A.R. 35(e) Announced August 7, 2025

Philip J. Weiser, Attorney General, Austin R. Johnston, Assistant Attorney General, Denver, Colorado, for Plaintiff-Appellee

Megan A. Ring, Colorado State Public Defender, Kira L. Suyeishi, Deputy State Public Defender, Denver, Colorado, for Defendant-Appellant ¶1 Mark Nielsen appeals his conviction on one count of reckless

manslaughter. We affirm.

I. Background

¶2 A jury could have reasonably found the following facts from

the evidence introduced at trial.

¶3 Nielsen and Danylle Shatto, who was Nielsen’s fiancée at the

time, lived together in a home (the residence) that Shatto rented

from her uncle John Achertkirch. Achterkirch and his

stepdaughter, J.J., later moved into the residence.

¶4 After J.J. moved into the residence, Shatto learned that J.J.

had an active arrest warrant. On July 28, 2020, Shatto reported

J.J.’s whereabouts to the police. J.J. was arrested only hours after

Shatto made her report.

¶5 When Achterkirch learned that J.J. had been arrested, he sent

angry text messages to Shatto. Nielsen and Shatto were alone in

the residence when Achterkirch sent the texts.

¶6 Shortly thereafter, Achterkirch returned to the residence and

announced that he “was going to kill [Nielsen and Shatto].” Shatto

and Achterkirch argued about J.J.’s arrest. Nielsen interrupted the

1 argument and said to Achterkirch, “Come on, let’s talk about this.”

In response, Achterkirch “knocked [Nielsen’s] head” onto a counter.

¶7 Achterkirch then said to Shatto, “I’m going to effing kill you.”

He approached her with his “hands out.” But before Achterkirch

could reach her, Nielsen drew a gun and fatally shot him.

¶8 Nielsen was charged with one count of second degree murder

and one count of the lesser included offense of reckless

manslaughter.

¶9 Before trial, the court denied Nielsen’s request for admission of

evidence of Achterkirch’s past violent acts toward women in his

family. Nielsen sought to introduce such evidence at trial to

support his self-defense theory.

¶ 10 At trial, defense counsel argued to the jury that Nielsen shot

Achterkirch in defense of himself and Shatto.

¶ 11 The jury acquitted Nielsen of second degree murder but

convicted him of reckless manslaughter.

¶ 12 On appeal, Nielsen contends that the court reversibly erred

and violated his constitutional rights by barring him from

presenting evidence of Achterkirch’s prior violent acts against

women in his family. In addition, Nielsen asserts that the court

2 plainly erred by not sua sponte instructing the jury to disregard

testimony that the court ruled was inadmissible. Lastly, Nielsen

argues that the court plainly erred by permitting the prosecutor to

commit misconduct during rebuttal closing argument and that the

cumulative errors at his trial require reversal of his conviction. We

disagree.

II. Analysis

A. The Court Did Not Err by Excluding Evidence of Achterkirch’s Prior Violent Acts

¶ 13 Nielsen contends that the court erred by barring him from

introducing evidence of Achterkirch’s prior violent acts against

women in Achterkirch’s family. We disagree.

1. Standard of Review

¶ 14 “We review a trial court’s evidentiary rulings for an abuse of

discretion.” Rojas v. People, 2022 CO 8, ¶ 16, 504 P.3d 296, 302.

“A trial court abuses its discretion when it misconstrues or

misapplies the law, or when its decision is manifestly arbitrary,

unreasonable, or unfair.” People v. Knapp, 2020 COA 107, ¶ 31,

487 P.3d 1243, 1252.

3 2. Additional Facts

¶ 15 Nielsen filed a pretrial notice that he intended to introduce

evidence of Achterkirch’s “past violent acts” to support his self-

defense theory. Nielsen identified two acts in the notice: a 2009

alleged domestic violence incident involving Achterkirch and his

then-wife (the DV incident) and Achterkirch’s alleged 2019 sexual

assault of J.J. (the sexual assault). Nielsen argued that he was

entitled to tell the jury about these acts because “evidence of a

victim’s prior violent acts may be introduced when the defendant is

asserting self-defense.” However, he did not explain the connection

between these acts and his assertion that he acted in self-defense

when he shot Achterkirch.

¶ 16 At a pretrial motions hearing, defense counsel orally amended

the notice to include the following allegations:

• J.J. told Nielsen about the sexual assault before the

shooting, although defense counsel did not say how long

before the shooting J.J. provided Nielsen with this

information, or that J.J. told him when the sexual

assault occurred.

4 • At the time of the shooting, Nielsen knew that

Achterkirch once threatened to throw J.J. out of a vehicle

and, on another occasion, had held a knife to J.J.’s

throat (the threats). Defense counsel did not specify

when Nielsen became aware of the threats or whether he

knew when Achterkirch made the threats.

• Nielsen “did not know any of the specific facts” about the

DV incident, “just that there was physical violence.”

¶ 17 The prosecutor objected to admission of evidence of the DV

incident, the sexual assault, and the threats (collectively, the prior

acts) because defense counsel did not indicate when or how Nielsen

became aware of them or when they occurred. The prosecutor

argued that the court lacked sufficient information to make the

findings necessary to admit evidence of the prior acts at trial. In

addition, the prosecutor asserted that evidence of the prior acts was

inadmissible under CRE 403 because it was “highly prejudicial.”

¶ 18 The court ordered defense counsel to submit an amended

notice of the prior acts and took the admissibility of the prior acts

under advisement.

5 ¶ 19 Nielsen’s counsel filed an amended notice consisting of a

single sentence:

Prior to July 28, 2020, [Nielsen] knew of the following incidents of violence perpetrated by [Achterkirch]:

That [Achterkirch] sexually assaulted [J.J.],

That [Achterkirch] was physically abusive to his [then-]wife,

That [Achterkirch] threatened to throw [J.J.] out of a moving truck, and

That [Achterkirch] at some point held a knife to [J.J.]’s throat.

Defense counsel did not provide any further information regarding

Nielsen’s awareness of the prior acts, such as when he specifically

learned about them or whether he knew when they occurred.

¶ 20 In ruling that evidence of the prior acts would be inadmissible

at trial, the court said it would “consider an offer of proof at any

time” and would “anticipate more substance at that juncture.”

Based on the limited information Nielsen had provided, the court

said that Nielsen failed “to offer the substance of how he knew of

the prior acts.”

¶ 21 The court concluded that the prior acts were inadmissible

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