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The Utah teen who pleaded guilty earlier this year to murdering his two younger brothers is facing new charges in adult court for allegedly assaulting another teen in a juvenile detention facility.

Aza Ray Vidinhar, 16, was charged Friday in Ogden's 2nd District Court with third-degree felony assault by a prisoner.

According to a probable cause statement filed in court, Vidinhar was arrested Thursday after he allegedly assaulted another boy at the Mill Creek Detention facility, located at 790 W. 12th Street.

Vidinhar allegedly "took a broom and attacked another male who is also in custody," according to the probable cause statement. Officers noted in the report that the other boy "did not fight back" and that Vidinhar allegedly initiated the fight. The alleged victim had minor bruises and scratches after the altercation.

Vidinhar pleaded guilty in June in juvenile court to one count of first-degree felony murder in connection with 10-year-old Alex Vidinhar's death, followed by a similar plea in adult court for killing his 4-year-old brother, Benjie Vidinhar.

The pleas were the result of an unusual plea agreement that allows the teen to be held in a juvenile facility until he is 21 years old, or until the juvenile system feels they can no longer help him.

At that time, defense attorney Todd Utzinger has said, the teen will be sentenced in adult court to a 15-years-to-life term at the Utah State Prison. The Utah Board of Pardons and Parole will then review the case, according to Utzinger.

It is not clear how the new felony charge will affect the plea agreement or Vidinhar's ability to stay in the juvenile system. If convicted as charged, the teen could be sentenced to another zero to five years in prison.

According to court records, the latest charge was filed in the adult court because Vidinhar had already been certified as an adult in the court system on one of the murder charges.

The teen's initial appearance on the new charge is set for Monday morning.

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.

A juvenile court judge agreed last year that the questioning violated the boy's Miranda rights, and said his statements could not be used against him in the case.

Davis County 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.

A motive for the slayings has never publicly been revealed.

Twitter: @jm_miller