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Teen suspects in fatal Colorado rock-throwing took photo of scene, became 'blood brothers' after attack, officials say

The three 18-year-olds took a picture of the deadly mayhem outside Denver before vowing silence in an incident that killed 20-year-old motorist Alexa Bartell, an affidavit says.

The teen suspects accused of hurling a large rock that killed a Colorado motorist took a photo of the deadly mayhem, then pledged a "blood brothers" oath to keep quiet about the crime, investigators alleged Thursday.

Nicholas “Mitch” Karol-ChikJoseph Koenig and Zachary Kwak, all 18, have all been booked on suspicion of murder. Arrest warrant affidavits painted a grisly picture of 20-year-old motorist's Alexa Bartell's death on a lonely stretch of Indiana Street in Jefferson County, between Denver and Boulder.

A hole in the windshield of Alexa Bartell's vehicle.
A hole in the windshield of Alexa Bartell's vehicle.Jefferson County Sheriff's Office

Bartell was on the phone with a friend, Jenna Griggs, at about 10:45 p.m. April 19 when the driver suddenly stopped speaking, Jefferson County sheriff’s investigator Daniel Manka wrote in an affidavit.

Griggs used the Find My iPhone feature to find Bartell's car with her friend inside, who had “sustained a significant injury to her head and was not moving,” according to the affidavit.

Griggs called Bartell’s mother and 911 before a Broomfield police officer arrived to find no pulse on the victim, whose arm was “cold to the touch,” the affidavit said.

Investigators found “biological matter” throughout the car and a large “‘river rock’ landscaping rock” on the side of the road, stained with blood, the affidavit said.

Several other motorists that night reported stones were hurled at their cars around the same time in the area where Bartell was fatally struck.

Sheriff’s investigators secured cellphone data pinging off four nearby towers and found one that had “passed in the area of the death of the victim at the same time that the victim, Alexa, stopped talking,” documents said.

The phone was linked to Koenig and his mother, Lara Koenig, investigators said.

A rock found by the roadway where Alexa Bartell was killed that tested presumptive positive for blood.
A rock found by the roadway where Alexa Bartell was killed tested presumptively positive for blood.Jefferson County Sheriff's Office

The probe's other major break came when detectives found a friend of Koenig’s, Joseph Bopp, 20, who said he was with the three suspects at a Walmart on April 19.

Bopp said that’s when he saw the three 18-year-olds “picking up landscaping rocks from the edge of the parking and putting them in the back seat of” Karol-Chik’s truck, the affidavit said.

“Joseph states that he knew something bad was going to happen, so he insisted they take him home, which they did,” according to court documents.

Karol-Chik told detectives that Kwak threw the stone that struck Bartell before Koenig turned the truck around to get a closer look at the damage.

Karol-Chik quoted Kwak saying, "We have to go back and see that (with emphasis on the word 'have')," the affidavit said.

“Joe slowed the vehicle so that Zach could take a photo of it. Mitch noted that he felt ‘a hint of guilt,’" the court document said.

Alexa Bartell.
Alexa Bartell.Jefferson County Sheriff's Office

Kwak initially told detectives he couldn’t remember events of that night but then "revised his statement" once he was confronted by Karol-Chik’s account to investigators, according to the affidavit.

Kwak said that the impact on Bartell’s car sounded like a “rail gun” and that he snapped a picture of the devastation because “he thought Joseph or Mitch would want it as a memento,” the affidavit said.

Kwak also told detectives that “Joseph and Mitch were talking about them now being ‘blood brothers’ and they could never speak of this incident,” court documents said.

“In addition, Zachary said that Joseph met with him the next day and tried to get their stories straight” so they could deny involvement, according to the affidavit.

A judge ordered all three to be held without bail.

The court documents and sheriff's deputies haven't said what might have motivated the deadly rock throw at Bartell.

Bopp told investigators that "Koenig frequently participates in destructive behavior" and "that he likes causing 'chaos.'"

Attorneys for all three defendants couldn't immediately be reached for comment Thursday.

CORRECTION (April 27, 2023, 10:25 p.m. ET): A previous version of this article and a headline misspelled the first name of the victim of the attack. She is Alexa Bartell, not Alex.