GOLDEN, Colo. -- A teen who allegedly confessed to the dismemberment killing of 10-year-old Jessica Ridgeway also sexually assaulted the Colorado girl, prosecutors said Tuesday.
Police say they arrested Austin Reed Sigg in connection with Jessica Ridgeway's death.
Austin Sigg, 17, was charged Tuesday as an adult with 17 counts in the Ridgeway case and in an attack on a jogger. They include four murder charges, kidnapping and sexual assault on a child.
Sigg didn't speak during the brief court hearing in Golden, Colo., and didn't look at his six relatives in the courtroom, including his mother, Mindy Sigg. His relatives sat silently as the charges were read, unlike a hearing last week at which Sigg's mother sobbed audibly. She was the one who called police on her son.
Family members of the slain child also watched the proceedings. Each wore purple, the girl's favorite color.
Defense attorneys anticipate asking the judge to send the case to juvenile court. If convicted as an adult, Sigg faces up to life in prison with the possibility of parole after 40 years. If he is tried as a juvenile, Sigg faces a maximum of seven years on each conviction, which, if ordered to be served consecutively, would put him in prison for decades.
Jessica Ridgeway, 10.
Prosecutors said Sigg acted alone in kidnapping, robbing and sexually assaulting Ridgeway. The robbery charge involved the girl's backpack and water bottle, which were found in another suburb three days after she disappeared while walking to school Oct. 5.
"Austin Reed Sigg unlawfully and feloniously, acting alone, committed sexual assault, and in the course of or in furtherance of that crime, caused the death of Jessica Ridgeway," according to court documents.
He is also charged in an attempted abduction of a 22-year-old woman near the girl's home months before the Ridgeway killing. Police said the jogger reported being grabbed from behind by a man who placed a rag with a chemical smell over her mouth. Police have not revealed whether the rag was soaked with a chemical meant to subdue the woman.
Police arrested Sigg on Oct. 23. His mother told The Associated Press that she called police and her son turned himself in.
Ridgeway lived on a quiet street about a mile from where Sigg lived with his mother. The subdivision features an elementary school, a high school, small parks, greenbelts, open space and a lake.
Sigg is being held without bond at a youth correctional facility. The charges filed were four counts of murder, two counts of kidnapping, sexual assault on a child and robbery in Jessica's abduction and slaying, as well as attempted murder, attempted sexual assault and attempted second-degree kidnapping in the attack on the runner. Prosecutors also charged Sigg with six counts of crime of violence.
"There's DNA evidence, and the evidence is overwhelming," prosecutor Hal Sargent said, arguing that Sigg should be held without bail despite having no criminal record.
Former high school classmates painted a picture of the 5-foot-6, 160-pound Sigg as an intelligent teen who often wore black and complained about school but who would stay late sometimes to work on computers. Sigg was interested in mortuary science and was taking forensics classes, according to classmates.
Sigg enrolled in August at Arapahoe Community College, which offers the state's only accredited mortuary science program. The school said Sigg didn't have enough credits yet to apply to that program.
Sigg had left Standley Lake High School in July after finishing the 11th grade and later earned a GED. School officials said they didn't know why he left. Former schoolmate Sarah Morevec said Sigg had been bullied for having a high voice.
The Associated Press contributed to this report.
More content from NBCNews.com:
- Volunteers rush in to help devastated region recover
- Sandy leaves NYC subway system, infrastructure licking its wounds
- 'There was no stopping it': Sandy's surge inundates northern NJ towns
- Breezy Point: 'Whatever is not flooded is on fire'
- By the numbers: Superstorm Sandy