GOLDEN, Colo. (AP) -- Prosecutors say a Colorado teenager has confessed in the abduction and killing of a 10-year-old girl and in a separate attack on a runner.

Authorities say they have "overwhelming" DNA evidence against 17-year-old Austin Reed Sigg.

Sigg made his first court appearance Thursday in the death of Jessica Ridgeway and an assault on a 22-year-old female runner in May. He kept head bowed for much of the time, talking with his attorney but otherwise saying little.

District Attorney Scott Storey said the law prevents prosecutors from seeking the death penalty because Sigg is a juvenile, even though he is being prosecuted as an adult.

Authorities have released few details about their investigation, and court documents have been sealed. A police custody report said Sigg was cooperative when he was arrested and waived his rights.