(CNN) -- A 17-year-old student was formally charged Tuesday with the kidnapping, sexual assault and murder of 10-year-old Jessica Ridgeway, whose body parts were found at a park in a Denver suburb earlier this month.
Austin Reed Sigg, a student at Arapahoe Community College, was also charged with attempting to kidnap, sexually assault and murder a female jogger last May.
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The charges were outlined in a 17-count accusation filed by Jefferson County, Colorado, District Attorney Pam Russell Tuesday.
Sigg, who lived about one mile from Ridgeway's home in Westminster, was charged as an adult, a decision that could be challenged by his lawyers.
The teen was arrested a week ago and accused of strangling Ridgeway, dismembering her and placing some of her body parts in a crawlspace under his family's home.
Police first found parts of her body at a park 5 miles away five days after the bespectacled blonde girl disappeared while walking to Witt Elementary School on October 5.
The big break in the investigation came last Tuesday night, when Sigg's mother called 911 and handed him the phone. Sigg, police said, confessed.
Along with charges related to Jessica's death, Sigg is also accused in the May assault of a 22-year-old woman on a hiking trail.
CNN's Shawn Nottingham contributed to this report.