Jefferson County Sheriff's Office
From left, Zachary Kwak, Nicholas Karol-Chik and Joseph Koenig all face murder charges in the killing of a 20-year-old woman.
CNN  — 

Three suspects were each charged with first-degree murder in the killing of a 20-year-old woman on a Colorado highway last month, who died after a large rock was allegedly thrown at her car and smashed through her windshield, prosecutors said Wednesday.

Nicholas Karol-Chik, Joseph Koenig and Zachary Kwak each face more than a dozen charges in total in the killing of Alexa Bartell, who was found dead in her car, and the injuring of three others as multiple moving vehicles were struck by rocks on the evening of April 19, according to a news release from the Colorado First Judicial District Attorney’s Office.

In addition to the murder charges, the suspects – all of whom were 18 years old at the time of arrest – also face six counts of attempted first-degree murder, three counts of second-degree assault and three counts of attempted second-degree assault.

The suspects have not entered pleas. CNN has reached out to their attorneys for comment.

Bartell was driving in northern Jefferson County, just northwest of Denver, when one of the suspects allegedly hurled a large landscape rock at her Chevrolet Spark, causing it to crash into a field, according to arrest affidavits.

After the deadly attack, Kwak – who allegedly threw the rock that killed the woman – said, “We have to go back and see that,” according to the affidavits. Kwak then snapped a photo of the crash, authorities say.

When police investigators asked why, Kwak said he thought Karol-Chik or Koenig “would want it as a memento,” according to the affidavit.

The day after Bartell’s killing, Koenig and Kwak met and “tried to get their stories straight about (what) happened, specifically denying involvement,” the affidavits said.

Jefferson County Sheriff's Office
Alexa Bartell, 20, was killed April 19 when a large rock was thrown at her car in Colorado.

Bartell was speaking on the phone with a friend when their conversation suddenly ended, according to police. Using the Find My iPhone app, her friend found Bartell and her phone in a field south of State Highway 128, the affidavits said.

The friend found Bartell motionless and with a significant head injury in the driver’s seat, according to the documents.

The suspects were allegedly involved in other incidents of throwing rocks at moving cars, the documents show. Karol-Chik and Koenig “have been involved in throwing objects since at least February on ten separate days,” Karol-Chik allegedly said.

The suspects are being held without bond in the Jefferson County Jail.

CNN’s Aya Elamroussi, Ray Sanchez, Michelle Watson, Sarah Dewberry and Rachel Webb contributed to this report.