Tyler W. Savage, 18, has been charged with aggravated first-degree murder in the death of 16-year-old Kimmie Daily. The charge could make Savage eligible for the death penalty if convicted.
Savage was arrested Monday evening after leading police to Kimmie's body, officials said.
Kimmie, who functioned at the level of a 9-year-old due to a disability since birth, disappeared August 17 after leaving her home to ride her bike to a friend's house.
Pierce County Prosecutor Mark Lindquist said Savage, who was an acquaintance of Kimmie, lured the girl to an isolated area near her home and strangled her to death when she tried to leave.
The teen also admitted to having sexual contact with Kimmie, Lindquist said.
According to prosecutors, Savage told investigators that that he dumped Kimmie's naked body in a thicket of blackberry bushes about 12 blocks from her house and threw her bicycle on top of her.
Savage told police that after the murder he went to a neighbor's house to play "Dungeons & Dragons" online in an effort to "forget," according to court documents.
"The rape and murder of Kimberly Daily, an innocent child and Special Olympian, is a horrible crime," Lindquist said in a written statement. "This is a tragic loss for Kimberly's family, her neighborhood, and the entire community."
While police spent the day searching for evidence at the scene where Kimmie's body was found, her family was still reeling from news of her death.
"We're just hanging in. It's all we can do," said Kimmie's grandmother, Naomi Daily. "Doing the best we can."
Savage's family left without comment, but a family spokesman said they've never had any trouble with Tyler Savage and need some time to sort things out.
"We will find out what happened soon, all of us, and we can go from there," said Michael Von Gnatensky.
Savage is currently being held in the Pierce County Jail without bail. He has an interim court appearance scheduled for Sept. 30 and his trial is scheduled to begin on Oct. 12.
Investigators told the News Tribune that the teen was going to be a senior at Emerald Ridge High School.
Kimmie's family and friends plan to hold a vigil tonight at Zieger Elementary at 8 p.m. The public is invited to attend.