The suspect, 17-year-old Austin Reed Sigg, appeared in court on Thursday in the death of Jessica Ridgeway and an assault on a 22-year-old female runner in May. Authorities say they have "overwhelming" DNA evidence against Sigg.
Sigg lived about a mile from Ridgeway, who disappeared Oct. 5 while walking to school. Her remains were found five days later in a field at a park. Sigg is being prosecuted as an adult, but District Attorney Scott Storey said the law prevents prosecutors from seeking the death penalty because Sigg is a juvenile.
He was taken into custody on Tuesday night after a phone call from his mother led authorities to Sigg. His mother told The Associated Press that he turned himself in.
"I made the phone call, and he turned himself in. That's all I have to say," said Mindy Sigg, before she broke down in tears and hung up.
Authorities said Sigg will also face charges in the May attempted kidnapping of the 22-year-old runner at the Ketner Lake Open Space. Police have said the two crimes are connected, but they haven't given further details.
In that case, a woman fought off a stranger who grabbed her from behind and put a rag that smelled of chemicals over her mouth, authorities said. Police have not determined if the substance on the rag was meant to subdue the woman.
The Associated Press contributed to this report.