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SALT LAKE CITY, Utah - An 18-year-old who was charged with sexually assaulting and murdering a 12-year-old girl in 2015 pleaded guilty in both juvenile and adult court Monday.

Police charged 18-year-old Jayden Sterzer with aggravated murder and rape of a child in July of 2015, but this is the first substantial move forward in this tragic case, according to KSTU.

The case has been essentially on hold since Sterzer was charged because his attorneys had been arguing that he didn’t understand the charges against him. However last month, juvenile court judge James Michie determined that Sterzer is now competent enough for the case to move forward.

On Monday, Sterzer’s attorney, Michael Sikora, announced that he will take a plea deal.

Back in July of 2015, police say Sterzer lured 12-year-old Kailey Vijil from her West Valley City home, asking her to help him look for his cat. Three hours later, her body was found in a horse pasture near her home. A medical examiner determined she had been sexually assaulted and strangled to death.

An attorney for the Vijil family, Spencer Banks, spoke to the media after court.

“There was really no resolution as I said that would be complete justice but they are satisfied with this resolution,” said Banks.

Sterzer’s attorneys announced that he’s taking a blended plea deal, meaning he’ll plead guilty to a lesser charge of murder and second degree felony forcible sexual abuse of a child in adult court. He’s also pleading guilty to rape of a child in juvenile court. This will allow him to be in a juvenile detention center until he turns 21, then he’ll be transferred to adult prison.

“Intellectually he operates at the level of about a third grader. It was just very important to try and do what we could to keep him in the juvenile system for the next three years because we just don’t think he was in any way, shape or form prepared for a lengthy stint at the Utah state prison,” says Sikora.

To try and explain the gravity of the situation, Judge Michie told Sterzer that he set in motion a series of events that he can’t undo. He said it’s like throwing a small rock into a pond causing ripples in the water, but in this case, Sterzer threw a boulder and it wasn’t ripples but waves.

Sterzer will be back in court on Jan. 19, 2018, where he’s expected to make a statement along with Kailey’s family before he’s officially committed to the juvenile facility.

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