The driver who had screamed at Meghan Bigelow on a busy suburban street and followed her and her three sons into the parking lot of a dental office to argue finally began to drive away. But then, Bigelow recalled Wednesday, Jeremy Webster stopped after she pulled out her phone to take a video of his car and got out with a gun.

Bigelow, testifying at the start of Webster’s murder trial, said she told her boys to run and began to walk away from them to try to keep Webster from hurting her children. She was shot in the back, and, after falling to the ground, shot in the head.

She said she heard her middle son, 12-year-old Cooper, call out for her and ask if she was OK. Not wanting to lie, she said, "I can hear you," so he would at least know she was still alive.

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Prosecutors said Webster, now 27, shot Bigelow’s two other sons, killing the oldest, 13-year-old Vaughn Bigelow Jr., and wounding the youngest, 8-year-old Asa, on June 18, 2018, in the Denver suburb of Westminster. Another man who witnessed the shooting during the road rage incident was also shot. Webster had "locked eyes" with the witness, John Gale, as he sat in his pickup truck waiting for an appointment with his 9-year-old daughter, Chief Deputy District Attorney Jennifer Prince told jurors during opening statements.

Webster has pleaded not guilty by reason of insanity in the shootings, which requires prosecutors to prove that he was sane at the time and knew the difference between right and wrong.

Jeremy Webster

Jeremy Webster, accused of killing a child and shooting others in a Colorado road rage incident, is seen in this booking photo taken on June 15, 2018. Webster is claiming insanity and pleaded not guilty the murder charges. (Westminster Police Department via AP,File)

Prince said that Webster, located and arrested with the help of the video Meghan Bigelow took, told detectives he had been losing his mind for years and it seemed like he had observed the shooting rather than being involved in it. A psychiatrist told police Webster, then 23, had been diagnosed with bipolar disorder and was prescribed antipsychotics and antidepressant medication, police have said. According to court documents, Webster said he had recently started taking a new medication that day.

However, Prince said Webster acted purposefully on the day of the shooting, hiding his handgun, which had been in the passenger seat, in a backpack in his trunk after the shooting and trying to kill Gale to cover up his actions as proof that he knew what he was doing.

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"The evidence will show the conscious decision-making before, during and after his crime," said Prince, who adds that Webster completed an errand at Home Depot after the shooting and returned to a worksite to finish a construction job.

As Prince talked about the shooting, Meghan’s husband, Vaughn Bigelow Sr., bowed his head at times or rested his head in his hands.

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Webster, wearing dress clothes, sat next to his lawyers, often writing on a yellow legal pad during testimony.

The defense did not provide an opening statement, which they are not required to do, and has not had the opportunity to present any witnesses yet.