One of the three teenagers accused of being involved in a spree of rock-throwing attacks last year that targeted seven drivers and killed 20-year-old Alexa Bartell pleaded guilty to three felony charges Friday.

Zachary Kwak, 19, pleaded guilty to first-degree assault, second-degree assault and criminal attempt to commit second-degree assault as part of a plea deal during a Friday disposition hearing in First Judicial District Court.

Bartell was killed on April 19, 2023, after a rock crashed through her windshield as she drove northbound on Indiana Street in Jefferson County. Three then-18-year-olds were arrested and accused of throwing rocks at seven vehicles that evening, including the one that killed Bartell.

In a sentencing addendum, prosecutors and the defense agreed to a minimum sentence of 20 years in the Department of Corrections and a maximum sentence of 32 years.

Kwak will not be sentenced to the Youthful Offender System — a medium security prison in Pueblo that houses male and female offenders between ages the ages of 14 and 19 — First Judicial District Judge Christopher Zenisek said in Friday’s hearing.

A sentencing hearing has been set for Sept. 3, and both bond and remaining jury trial dates have been vacated, Zenisek said Friday.

In previous hearings, prosecutors said that despite not being able to tell who threw which rocks, all three men — Kwak, 19-year-old Joseph Koenig and 18-year-old Nicholas “Mitch” Karol-Chik — were complicit because there was “excitement” in the truck as they drove around the night of April 19 and the teens cheered after the rock hit Bartell’s vehicle, Jefferson County sheriff’s Detective Dan Manka testified.

Koenig’s next hearing is scheduled for July 3 and his jury trial is set to begin on July 19, according to Jefferson County Court records. Karol-Chik has a disposition hearing May 15 and his jury trial is scheduled to begin on June 7.

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