At that time, Utzinger said, the teen will be sentenced in adult court to a 15-year-to-life term at the Utah State Prison. Utzinger said they will then ask the Utah Board of Pardons and Parole to review the case.
The plea agreement was satisfactory to both Vidinhar's defense team and prosecutors allowing the teen to get therapy and treatment in the juvenile system, but also protecting the public with the option of keeping him incarcerated into his adult years, if needed.
If Vidinhar's case had stayed entirely in juvenile court, he would have had to be released from a juvenile facility when he turned 21, prosecutors have said.
"Without the opportunity and benefit of treatment, it would be my opinion that it's inhumane to send him to prison," Utzinger told 2nd District Judge David Hamilton on Wednesday just before Vidinhar pleaded guilty in adult court.
Prosecutors have said they wanted to have the teen tried in adult court, but Deputy Davis County Attorney Ryan Perkins told Hamilton that they were satisfied with Wednesday's plea agreement.
"We're very happy with this resolution, considering the difficult circumstances," Perkins said.
Until now, The Salt Lake Tribune has not named Vidinhar, consistent with the newspaper's policy of not naming juvenile criminal suspects. But that stance changed in light of the defendant's guilty plea in adult court and the pending prison term.
Vidinhar, handcuffed and dressed in a sweatshirt and sweatpants, did not make a statement in court, speaking only in response to the two judges' questions.
When Judge Frost asked if on May 22, 2013, the teen had knowingly and intentionally killed his brother with multiple stab wounds, Vidinhar replied, "That's true," as his parents, sitting in the court gallery, dabbed tears from their eyes.
Outside of court, Utzinger told news reporters that it was a difficult day for Vidinhar's parents, but he said that they supported the resolution.
"They are in an impossible situation," he said. "They're trying to balance their love for Aza and their other children and how to handle an event of this magnitude, and I think they've done very well."
Utzinger said Wednesday was a "somber day," but that the plea resolution "hopefully will give Aza an opportunity to get treatment and still protects the state's interest in having society remain safe until we know how well Aza does."
Prosecutors left the courthouse Wednesday without making any comments, but a press release was later issued by the office that detailed the plea agreement.
"Under this resolution, Aza will receive the benefits of resources available in the juvenile justice system as he matures," the statement reads. "In addition, public safety concerns are addressed by moving Aza into the adult system when he has completed his juvenile court sentence. The adult Board of Pardons will ultimately decide if and when he may be released from prison."
Davis County Attorney Troy Rawlings said Wednesday afternoon that the decision to plead guilty to charges in both juvenile and district court is unusual, but not unheard of. He said some sex abuse cases have been resolved this way in other Utah district courts, but he was not aware of any other murder case that was resolved in this fashion.
"It's absolutely true that he will get better services in the juvenile system," Rawlings told The Tribune. "But there's no way we were willing to take the risk [of release at 21 years old.] He poses, in our view, an unacceptable risk to the public."
Vidinhar was arrested the night of May 22, 2013, after his mother called 911 to report finding her 4-year-old son dead on the floor of her West Point home. She said Aza Vidinhar, then 15, and her 10-year-old son were both missing.
Sheriff's deputies subsequently found the 10-year-old's body in another part of the house. Both victims suffered "penetrating knife wounds," Davis County Sheriff Todd Richardson has said.
Officers later found Vidinhar walking in Layton, about 8 miles from his home. He was taken to a hospital and then to the Davis County Sheriff's Office interrogation room for what would become a controversial interview.
Vidinhar was held for questioning into the next morning and pressured by four detectives to give statements, even though he refused multiple times and fell asleep twice, his defense attorneys claimed.
Frost in November agreed that the questioning violated the boy's Miranda rights, and said his statements could not be used against him in the case.
Prosecutors have declined to discuss what Vidinhar said or how the loss of those statements affected their case. But they have said that certain other spontaneous statements made by the teen could still have been used against Vidinhar, according to attorneys and court documents. Also, police have said that traces of blood found on the teen linked him to the crime scene.
Vidinhar has been held at the Farmington Bay Youth Detention Center.
He has no prior criminal history, according to court officials.
Prior to Wednesday's resolution, Frost had been deciding whether the teen's certification hearing to determine if his case would remain in juvenile court or be sent to adult court would be open to the public. But the teen's plea deal made that issue moot.
Utzinger had filed a motion in May asking that the three-day certification hearing scheduled to begin June 25 be closed to media and public observers.
Utzinger told the judge that the hearing would cover sensitive issues, such as the teen's psychological evaluation and his family history.