GOLDEN, Colo. -- Prosecutors say a teenager who allegedly confessed to killing a 10-year-old Colorado girl and attacking a runner also sexually assaulted the girl.

Seventeen-year-old Austin Sigg was charged as an adult with 17 counts in both cases Tuesday. They include four murder charges.

Sigg didn't speak during the brief court hearing in Golden and didn't look at his six relatives in the courtroom that included his mother, Mindy Sigg. His relatives sat silently as the charges were read, unlike the hearing last week where Sigg's mother sobbed audibly.

Eight relatives of Jessica Ridgeway, of Westminster, also watched the proceedings, including her mother. Each wore purple, Jessica'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.

In charging documents, prosecutors said Sigg acted alone in kidnapping, robbing, and sexually assaulting Jessica. The robbery charge involved Jessica'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.

Police arrested Sigg on Oct. 23 after his mother told The Associated Press that she called police and her son turned himself in.

Jessica 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 at a hearing Thursday, arguing that Sigg should be held without bail despite having no criminal record.

Police said the runner 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.

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 don't know why he left.

Former schoolmate Sarah Morevec said Sigg had been bullied for having a high voice.

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  • Austin Reed Sigg

    This booking photo released by the Westminster, Colo., Police Department shows Austin Reed Sigg. Police in this Denver suburb announced Wednesday, Oct. 24, 2012, that Sigg, 17, has been arrested in the abduction and killing of a 10-year-old girl and the attempted kidnapping of a runner. Police say they arrested Sigg at his Westminster home Tuesday night, about five miles from the home of Jessica Ridgeway, who disappeared Oct. 5. Her body was found five days later in a field at a park. The break comes two days after police said Jessica's abduction was linked to the attempted abduction in May of a 22-year-old runner at another park. (AP Photo/Westminster Police Department)

  • Westminster Police Chief Lee Birk, center, and Jefferson County District Attorney Scott Storey, right, announce the arrest of Austin Reed Sigg,17, for the murder of Jessica Ridgeway at the Westminster Police Station Wednesday, Oct. 24, 2012 in Westminster CO.. (AP Photo/Barry Gutierrez)

  • The Westminster PD Command Post

    From the <a href="http://www.facebook.com/photo.php?fbid=10151346946994305&set=pb.141296864304.-2207520000.1350415448&type=1&theater">Westminster Police Department's Facebook page</a> describes the team of people looking for Jessica Ridgeway's killer: <blockquote>A snapshot of local, state and federal agencies working together in the Westminster PD Command Post. Hundreds of officers will be working throughout the weekend.</blockquote>

  • This undated evidence photo provided by the Westminster Police Department shows a wooden cross recovered by police, showing three vertical lines etched into the cross. Authorities are looking for someone who may carry or wear this type of cross, may have recently purchased one of these, or is known to have some association with one. Police are searching this and other links between the abduction and slaying of 10-year-old Jessica Ridgeway and the attempted abduction of a 22-year-old woman at a neighborhood lake in May. (AP Photo/Westminster Police Department)

  • Jefferson County District Attorney Scott Storey addresses the media during the announcement of the arrest of Austin Reed Sigg,17, for the murder of Jessica Ridgeway at the Westminster Police Station Wednesday, Oct. 24, 2012 in Westminster Colo. (AP Photo/Barry Gutierrez)

  • Brooke Olds, 13, stands on the street where she would play frequently, see or talk to Austin Reed Sigg who she knew since she was four years old. "He (Sigg) would play capture the flag with us. He always wanted to hang out with us girls, " Olds said. Sigg lived down the street from Olds and was arrested for the murder of Jessica Ridgeway Wednesday, Oct. 24, 2012 in Westminster, Colo. (AP Photo/Barry Gutierrez)

  • Brooke Olds, 13, stands on the street where she would play frequently, see or talk to Austin Reed Sigg who she knew since she was four years old, in Westminster, Colo., Wednesday, Oct. 24, 2012. Olds said she usually saw Sigg alone on a skateboard or scooter. “He was shy and kept to himself,” she said. Sigg lived down the street from Olds and was arrested for the murder of Jessica Ridgeway. (AP Photo/Barry Gutierrez)

  • Investigators remove items from what is believed to be Austin Reed Sigg's home at 10622 102nd Avenue Wednesday, Oct. 24, 2012 in Westminster, Colo. Sigg is being held for the murder of Jessica Ridgeway. (AP Photo/Barry Gutierrez)

  • Jefferson County District Attorney Scott Storey speaks during the announcement the arrest of Austin Reed Sigg,17, for the murder of Jessica Ridgeway at the Westminster Police Station Wednesday, Oct. 24, 2012 in Westminster, Colo. (AP Photo/Barry Gutierrez)

  • Westminster Police Chief Lee Birk, center and Jefferson County District Attorney Scott Storey, left, walk out to announce the arrest of Austin Reed Sigg,17, for the murder of Jessica Ridgeway at the Westminster Police Station Wednesday, Oct. 24, 2012 in Westminster CO.. (AP Photo/Barry Gutierrez)

  • Westminster Police Chief Lee Birk, center, and Jefferson County District Attorney Scott Storey, right, announce the arrest of Austin Reed Sigg,17, for the murder of Jessica Ridgeway at the Westminster Police Station Wednesday, Oct. 24, 2012 in Westminster CO.. (AP Photo/Barry Gutierrez)

  • Missing School Girl

    This image provided by the Westminster Colorado Police Department shows 10-year-old Jessica Ridgeway. Police in Westminster are looking for a 10-year-old girl who was last seen walking to school. Jessica Ridgeway normally meets a friend at a park on her way to Witt Elementary School, but she didn’t make it to the park or school Friday Oct. 5, 2012. An Amber Alert has been issued. (AP Photo/Westminster Colorado Police Department)

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • 150105_10151341575584305_1291829664_n

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    Via <a href="http://www.facebook.com/media/set/?set=a.10151340500824305.521112.141296864304&type=1">Westminster PD's Facebook page</a>.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Department released new photos of missing 10-year-old Jessica Ridgeway. The picture is dated June 25th, 2011.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is dated July 6, 2006.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo of Jessica is dated July 13, 2006.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Jessica Ridgeway

    The Westminster Police Dept. provided <a href="http://www.facebook.com/pages/Westminster-PD/141296864304">new photos of missing 10-year-old Jessica Ridgeway on their Facebook page</a> Tuesday. Jessica has been missing since Friday Oct. 5th. This photo is undated.

  • Arvada Police spokeswoman Jill McGranahan, left, and Westminster Police spokesman Trevor Materasso, right, address the media regarding a body found lat Wednesday in Parttridge Park in Arvada during a press conference at the Westminister Police Department Thursday, Oct. 11, 2012 in Westminister, Colo. The search missing 10-year-old Jessica Ridgeway will continue, police said Thursday. (AP Photo/Barry Gutierrez)

  • Missing School Girl

    A police officer walks through a field of tall grass searching for ten-year-old Jessica Ridgeway near her home in Westminster, Colo., on Monday, Oct. 8, 2012. The youngster has been missing since she left her home Friday morning on her way to school. (AP Photo/Ed Andrieski)

  • Missing School Girl

    Denis McLaughlin leads his search and rescue dog through a field of tall grass searching for ten-year-old Jessica Ridgeway near her home in Westminster, Colo., on Monday, Oct. 8, 2012. The youngster has been missing since she left her home Friday morning on her way to school. (AP Photo/Ed Andrieski)

  • Missing School Girl

    Members of a search and rescue team use a dog while searching for ten-year-old Jessica Ridgeway near her home in Westminster, Colo., on Monday, Oct. 8, 2012. The youngster has been missing since she left her home Friday morning on her way to school. (AP Photo/Ed Andrieski)

  • Missing School Girl

    A member of a search and rescue team leads his dog through a field of tall grass searching for ten-year-old Jessica Ridgeway near her home in Westminster, Colo., on Monday, Oct. 8, 2012. The youngster has been missing since she left her home Friday morning on her way to school. (AP Photo/Ed Andrieski)

  • Missing School Girl

    A Westminster police officer sits in her partrol car at the home of ten-year-old Jessica Ridgeway in Westminster, Colo., on Monday, Oct. 8, 2012. The youngster has been missing since she left her home Friday morning on her way to school. (AP Photo/Ed Andrieski)

  • Missing School Girl

    A missing poster for ten-year-old Jessica Ridgeway is seen in Broomfield, Colo., on Monday, Oct. 8, 2012. The youngster has been missing since she left her home Friday morning on her way to school. (AP Photo/Ed Andrieski)

  • Arvada Police spokeswoman Jill McGranahan, left, and Westminster Police spokesman Trevor Materasso, right, address the media regarding a body found lat Wednesday in Parttridge Park in Arvada during a press conference at the Westminister Police Department Thursday, Oct. 11, 2012 in Westminister, Colo. The search missing 10-year-old Jessica Ridgeway will continue, police said Thursday. (AP Photo/Barry Gutierrez)

  • Police search near an area where a body was found Wednesday in Parttridge Park, in Arvada, Colo., during the ongoing search for missing 10-year-old Jessica Ridgeway on Thursday, Oct. 11, 2012. Police are not saying whether the body found is linked to the missing girl case and noted Thursday that officers are still searching for Ridgeway, who disappeared Oct. 5. (AP Photo/Barry Gutierrez)

  • Police search near an area where a body was found Wednesday in Parttridge Park, in Arvada, Colo., during the ongoing search for missing 10-year-old Jessica Ridgeway on Thursday, Oct. 11, 2012. Police are not saying whether the body found is linked to the missing girl case and noted Thursday that officers are still searching for Ridgeway, who disappeared Oct. 5. (AP Photo/Barry Gutierrez)

  • Police search near an area where a body was found Wednesday in Parttridge Park, in Arvada, Colo., during the ongoing search for missing 10-year-old Jessica Ridgeway on Thursday, Oct. 11, 2012. Police are not saying whether the body found is linked to the missing girl case and noted Thursday that officers are still searching for Ridgeway, who disappeared Oct. 5. (AP Photo/Barry Gutierrez)

  • Police search near an area where a body was found Wednesday in Parttridge Park, in Arvada, Colo., during the ongoing search for missing 10-year-old Jessica Ridgeway on Thursday, Oct. 11, 2012. Police are not saying whether the body found is linked to the missing girl case and noted Thursday that officers are still searching for Ridgeway, who disappeared Oct. 5. (AP Photo/Barry Gutierrez)