All it took was 10 minutes. That’s the span of time between when Jeremy Webster, 23, and Meghan Bigelow, 41, had an angry exchange on a busy street in Westminster, Colorado on Thursday. Webster then followed Bigelow, who was in the car with her three sons, as she pulled into a parking lot about a mile away. After a short argument Webster decided to pull out his Glock 19 handgun.

That’s when Webster allegedly went on to shoot Meghan Bigelow several times before aiming his gun at Vaughn Bigelow, 13, and his eight-year-old brother, Asa, and pulling the trigger multiple times. The 12-year-old son, Cooper, managed to escape unscathed and recounted the incident to police. Vaughn Bigelow died while his mom and eight-year-old brother were in critical condition at a hospital. A bystander, John Gale, was shot on both arms while he was in his truck with his nine-year-old daughter. He is recovering.

“Through our investigation we have been able to determine the suspect did not know any of the victims and did not have a relationship with any of them,” the Westminster Police Department said in a statement. “It appears as if this incident stemmed from a road rage.”

The son who was unscathed told police his mom had taken a photo of the license plate of the car that had been following them. That helped police track down Webster, who told police he “has mental health issues” and that he started taking a new prescription medication shortly before the incident. “Jeremy eventually admitted that he was the one who shot Meghan, both of her children and John Gale,” according to the affidavit.