Savoie entered a guilty plea to second-degree murder in the death of 13-year-old Craig Sorger, KXLY-TV of Spokane reported.
Sorger was stabbed to death in Ephrata in 2003 in a case that drew wide attention.
Savoie was originally convicted of first-degree murder, but his conviction was later overturned because of a trial error. He was scheduled to go on trial again next year.
This is the first time that Savoie, who is now 23, has admitted to killing Sorger, KXLY reported.
Savoie could be given 12 to 21 years in prison when he's sentenced next year.
Sorger's body was found in an Ephrata recreational vehicle park, the victim of a beating and stabbing so brutal the tip of a knife was left in his skull. His alleged assailants were two 12-year-old playmates. They proclaimed their innocence before one agreed to testify against his friend in a plea deal.
In 2011, the Washington state Court of Appeals threw out the conviction on a judge's error and ordered a new trial, to the dismay of the victim's family, prosecutors and community leaders.
Sorger was last seen playing with two 12-year-olds, Jake Eakin and Evan Savoie, and his mother reported him missing when he didn't return home. Police found his body in a mix of brush and leaves at an RV park.
A medical examiner determined he had been beaten and stabbed 34 times.
Police said there were discrepancies in the playmates' stories and blood on their clothing. The youths proclaimed their innocence for two years, even appearing on national television, but Eakin ultimately led police to the murder weapon -- a knife that matched the missing tip -- and agreed to testify against Savoie in a plea deal.
Prosecutors tried Savoie as an adult, one of the youngest such defendants in state history, and a jury convicted him of first-degree murder.
The case ultimately cost the county and the state, which pitched in to help pay for the high-profile trial, more than $1 million.
The appeals court overturned the guilty verdict and ordered a new trial on grounds that the judge violated Savoie's right to a public trial by closing the courtroom to hear arguments on a motion.
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