Stone-faced and clad in an orange jumpsuit, 20-year-old Zachary Kwak sat at the witness stand in a Jefferson County courtroom Thursday ready to implicate his co-defendant on a murder charge.

“I didn’t want to be a part of what was about to happen,” he told the jury about the minutes before the death of 20-year-old Alexa Bartell. 

Kwak, a co-defendant in the case connected to the death of Bartell in 2023, took the stand to detail the events leading up to the death that resulted in the first-degree murder trial of 20-year-old Joseph Koenig. Kwak’s testimony came as part of a plea agreement with prosecutors, in which he avoided trial on murder charges and will spend no more than 32 years in prison on a first-degree assault conviction.

Koenig, Kwak and Nicholas “Mitch” Karol-Chik were arrested six days after Bartell’s death on April 19, 2023, all initially charged with first-degree murder.

Around 11 p.m. the night of her death, Bartell was driving to her girlfriend’s home after being at a friend’s house when a landscaping rock smashed through her driver’s side window, immediately killing her.

The incident happened near the 10600 block of Indiana Street near Rocky Flats Wildlife Refuge.

Kwak claimed that Koenig had sped up to 103 mph before shot putting the rock toward Bartell’s Chevrolet Spark, creating a sound he described as artillery fire.

“Oh my god,” Greg Bartell, Alexa’s father, exclaimed after hearing the speed, breaking into deep sobs.

“All I could see was the black road, the black sky and bright red taillights. After that, I saw a car turn gently off the road,” Kwak said.

Bartell’s car then drove through a fence and around 200 feet into a nearby field.

The trio drove past the scene three times, with Kwak taking a picture.

In opening statements, the prosecution called the photos “mementos” for the trio, but Kwak said they were just to observe the extent of the vehicle’s damage.

The deadly incident was not the first time that the trio threw rocks from a moving vehicle, according to Kwak.

Chief Deputy District Attorney Katharine Decker claimed that Koenig and Karol-Chik had thrown rocks and other heavy objects from moving vehicles multiple times between February and Bartell’s death — information First Judicial District Judge Christopher Zenisek allowed to be presented to jurors at the trial. 

Decker claimed that the group hit 10 vehicles with rocks over three separate nights between February and April, with the final rock being the one that struck Bartell. 

The previous victims also testified during the trial, detailing the multiple incidents in which their windshields or bumpers were struck by random, flying rocks. 

Kwak claimed to have met the duo a few weeks prior to Bartell’s death, with the April 19 incident being the first time he threw rocks with them.

He said they collected rocks at a Walmart, dropped off a fourth friend and began throwing rocks at parked vehicles. Kwak, who was seated behind Karol-Chik on the passenger side, said he never threw a rock and only handed them to the two up front.

He claimed to have told the duo he wanted to go home, but Karol-Chik said: “You’ll go home when we want you to go home.”

The defense noted that Kwak didn’t press the issue of going home and continued to help them collect rocks. Kwak even ran into other friends when collecting rocks and didn’t ask them to take him home. 

When asked by Decker why he didn’t throw rocks, Kwak said it didn’t seem right to him.

When asked by Koenig’s defense attorney, Thomas Ward, if the plan was to hurt people, Kwak said no — a main pillar of the defense’s case. The defense has argued that the trio were just pulling pranks, like flipping trashcans and messing with car mirrors, with no intent to harm people.

During opening statements, Ward called the rock throwing reckless, dangerous and “incredibly stupid,” but not first-degree murder.

Koenig and Karol-Chik allegedly cheered and whooped after each hit, with the throws progressing to moving vehicles. While Kwak did not know what sparked the escalation, he said things escalated even further, with Koenig eventually starting to speed up before hurling the rocks from the truck.

After the rock hit Bartell’s car, Koenig didn’t cheer, according to Kwak. Despite seeing blood on the road, no one called 911.

“Something seemed different,” he said, but still claimed that Koenig seemed excited about the incident. 

The duo allegedly told Kwak that they were now “blood brothers” and they could never tell anyone about the incident.

“There was concern in the car, but I couldn’t tell you if it was mostly for self or for her,” he said.

The next day, Kwak met with Koenig after school to discuss the death, when Koenig allegedly told Kwak never to speak about it even to police.

During opening statements, Ward alleged that Kwak actually threw the rock that killed Bartell — though it truly doesn’t matter to the outcome of the trial, with the prosecution only needing to prove that Koenig was complicit to the death.

During the testimony, Ward quoted Karol-Chik’s previous interview where he allegedly told Kwak the rock was too big when he was picking it out. Kwak allegedly told Karol-Chik that if no one would throw it, he would.

Kwak denied saying this.

Kwak told investigators after his arrest that he did not know why he was arrested and did not know where he was that evening. He only admitted that Koenig threw the rock after investigators told him they had proof that he did it.

Furthermore, Karol-Chik allegedly told investigators Kwak threw the rock three times throughout various interviews. The fourth time, he said Koenig did it.

Kwak and Karol-Chik eventually struck plea deals with the First Judicial District Attorney’s Office, which Ward called “sweetheart deals” during opening statements.

Karol-Chik pleaded guilty to second-degree murder and attempted first-degree murder, facing a possible prison sentence between 35 and 72 years.

Kwak pleaded guilty to first-degree assault, multiple counts of second-degree assault and attempted second-degree assault, with a prison sentence between 20 to 32 years.

Both also agreed to testify against Koenig as part of the deal. They will both be sentenced after Koenig’s trial, which is expected to take another week.

Koenig is charged with one count of first-degree murder, nine counts of attempted first-degree murder, three counts of second-degree assault and six counts of attempted second-degree assault. The defense wants the most serious charge dropped to manslaughter. 

The trial will continue Friday morning with Karol-Chik set to testify in the next few days.