3 arrested for 1st-degree murder in Colorado rock-throwing incidents that killed 20-year-old driver

Three suspects have been arrested for allegedly throwing large landscaping rocks toward at least seven cars on Colorado roads last week, authorities said. The last of the seven incidents claimed the life of 20-year-old driver Alexa Bartell.

The suspects, all 18-year-old high school seniors, were taken into custody at their parents' homes in Arvada overnight and are all facing charges of first-degree murder, with extreme indifference, the Jefferson County Sheriff's Office announced Wednesday morning. Additional charges are expected, authorities said.

It's not clear which suspect or suspects -- identified as Joseph Koenig, Nicholas "Mitch" Karol-Chik and Zachary Kwak -- were driving during the spree, but all three are suspected of throwing rocks, authorities said. It appears they threw the rocks while driving, authorities said.

Around 10:45 p.m. on April 19, Bartell was driving when someone threw a large rock through her windshield, hitting and killing her, the sheriff's office said.

In the hour before Bartell was killed, six other cars in the area had rocks thrown at them, according to the sheriff's office. In two of those incidents, the drivers suffered minor injuries.

Nathan Tipton, a Lyft and Uber driver, was one of the four uninjured victims.

"When I found out that this series of events actually took a young lady's life, I feel for Alexa and her family. It put me in a bit of a shock. My wife, it really got to her," he told reporters on Tuesday.

"Nobody should lose their child for a random act. ... It's heartbreaking," said Tipton, a dad of three.

The sheriff's office said phone forensics and information from the public helped lead to the arrests.

As the three suspects made their first court appearance on Thursday, prosecutors said the community is outraged, and that the teens' reckless and irresponsible actions took away "an innocent life."

The teens, who were held on no bond, are set to return to court on May 3.

ABC News' Jenna Harrison and Alex Stone contributed to this report.