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A 17-year-old boy suspected in the brutal 2012 slaying of a Draper teenage girl has waived extradition from Colorado and been returned to Utah, where prosecutors say they will seek to have him tried as an adult for murder.

Salt Lake County District Attorney Sim Gill on Tuesday confirmed that the boy, who had been living in Grand Junction, Colo., had decided not to fight extradition, and that he was currently being held in a county juvenile detection center.

"Given the seriousness of the alleged crime, we have decided to certify him [for trial in adult court]," Gill said, noting that his staff was preparing to argue that motion in juvenile court at some point in the near future.

The 17-year-old boy is the same youth who, then 14, initially denied having seen his girlfriend, 15-year-old Anne Kasprzak, the night she secretly slipped out of her home. Her body, battered beyond recognition — DNA ultimately identified her — was found in the Jordan River three days later, on March 11, 2012.

In conjunction with the arrest, Gill's office filed charges of first-degree felony murder and second-degree felony obstruction of justice against the teen.

The Salt Lake Tribune generally does not name juvenile defendants unless they have been certified to stand trial as an adult.

A probable cause statement filed in 3rd District Juvenile Court lays out some of the evidence against the teen.

It says Kasprzak's phone records show numerous calls to and from the defendant between 7 and 8:30 on the night of her disappearance. After 8:30 p.m., he never called Kasprzak again, according to the statement.

Police spoke to the defendant a few days after Kasprzak's body was found and asked for the shoes he was wearing. He told officers that Kasprzak had a bloody nose two weeks before at the home of one of his friends and that some of the blood dropped onto a shoelace, the probable cause statement says.

During an interview with officers, the friend at first said Kasprzak had a bloody nose at his house, the statement says. But after officers located a text on the friend's phone from the defendant asking him to tell police the bloody nose story, the friend admitted he had lied, the statement says.

The friend also said that the defendant told him he had been at the Jordan River that night but not to tell anyone and also instructed him to erase the messages on his phone, according to the statement.

"The defendant's shoes were tested and human blood was located in multiple areas on both shoes," the statement says. "Further testing on the human blood on both shoes yielded a DNA profile which matches the DNA profile of Anne Kasprzak."

In addition, officers reassembled a piece of shredded paper they found in the defendant's trash can that contained notes "with facts about the case, a rough timeline, and a line describing a jacket 'she' was wearing 'that night,' " the probable cause statement says. It says Kasprzak's mother confirmed that a jacket her daughter owned, matched the description in the note, was missing.

The probable cause statement also says that Veronica Kasprzak called the defendant at 9:01 p.m. on March 10, 2012, while looking for her daughter. The boyfriend said he had not seen the girl and did not know where she was, the statement says.

An analysis of cell tower data shows the defendant was within 100 meters of the crime scene, according to the statement.

Twitter: @remims