"I can only imagine the kind of trauma that creates," Holtan said of theSept. 1shooting, which he described as "chaos."
Walker, 34, also was set to make his initial appearance Monday, but was not transported to Judge Royal Hansen's courtroom at the request of his attorney, Denise Porter, who told the judge that medical concerns prevented him from appearing.
After allegedly shooting Johnson and Vaillancourt, Walker shot and wounded himself in the head. Salt Lake District Attorney Sim Gill said Monday that Walker sustained "a lot of trauma to his mouth and jaw," which may affect Walker's ability to communicate verbally.
"It certainly has no bearing on our analysis of filing the charges," Gill said of Walker's injuries. "So from our perspective, it has no bearing whatsoever."
Walker is charged with first-degree felony aggravated murder for Johnson's death. He is also charged with attempted homicide for allegedly trying to kill Vaillancourt his girlfriend during the same shooting episode, along with three counts of discharge of a firearm and one count of possession of a weapon by a restricted person, all third-degree felonies.
Vaillancourt is charged with two counts of obstruction of justice for allegedly lying to investigators about the incident. She was wheeled into court Monday in a wheelchair, and was breathing with the aid of an oxygen tank. She said very little during the brief appearance, only speaking when asked to verify the spelling of her name and date of birth with the judge.
Vaillancourt and Walker are both expected back in court again on Oct. 8 in West Jordan.
For Victoria King, it was the first time she had seen Vaillancourt her sister since the shooting.
"It was hard," King said outside of court. "My heart still bleeds for Johnson's family ... It hurts to see her like that."
King has said her relationship with her sister became strained over the last decade as Vaillancourt struggled with addictions that began when she started taking painkillers to deal with swelling from a blood disorder.
"She's my sister, and I love her," King said. "I just don't love the choices she's made."
According to charging documents, Johnson, 32, was in a marked Draper City police vehicle at about 6 a.m., when he stopped at 13200 South Fort Street and noticed Walker standing outside his stopped Volvo.
Authorities said Walker had stopped because he ran out of gas and the passenger-side front tire had gone flat because he had driven over a curb, a stop sign, a large rock and then through at fence at 13800 S. 933 East, court records show. He then continued driving a few blocks away to the area of 13200 South, police said.
When Johnson pulled up near the Volvo to see if he could help, Walker allegedly shot Johnson through the open front passenger side window of Johnson's police vehicle.
Johnson was struck in the chest by the bullet and tried to drive away northbound. Walker, who was allegedly under the influence of methamphetamine at the time, fired at least three more shots, which struck Johnson's marked vehicle, court documents state.
Johnson used his police radio to call "shots fired," but then lost control of his vehicle and crashed into a wooded area about two blocks north of where he was shot.
The medical examiner later determined Johnson died from a gunshot wound to the chest.
Gill has said Johnson was wearing a bulletproof vest, but the bullet struck in an area the vest did not cover.
Walker was hospitalized for his injuries before being booked into the Salt Lake County jail last Wednesday, where he remains in lieu of $2 million cash-only bail.
Vaillancourt was released from a hospital late Saturday and booked into the Salt Lake County jail. Her bail has been set at $500,000 cash-only.