Police in the Denver suburb of Westminster took Sigg into custody on Tuesday night after receiving a phone call, from his mother, that led them to Sigg. He was formally arrested Wednesday.
Sigg reportedly told his mother that he was responsible for the murder of the 10-year-old who was abducted while walking to school. Part of her dismembered remains were found five days later in a field at a park. The torso was reportedly found on Oct. 10. Her remains weren't identified until Oct. 12 because of the body's condition.
Police released photos of a cross apparently left behind by Jessica's killer.
"I made the phone call, and he turned himself in. That's all I have to say," his mother, Mindy Sigg, told a reporter before she broke down in tears and hung up.
Investigators say Sigg also admitted to having some of the 10-year old's remains in a crawl space in his home. Authorities reportedly have recovered those remains since Sigg's arrest.
A Denver television station reported that Sigg in his confession told police he didn't receive the joy from fatally strangling her that he thought he would, so he went further.
Sigg attended Witt Elementary - the same school Jessica went to - but he moved on to middle school in 2007, before she enrolled at Witt, Jefferson County Public Schools spokeswoman Lynn Setzer said.
Authorities declined to elaborate on the arrest and have released few details about the case. Court documents have been sealed, but a police custody report said Sigg was cooperative when he was arrested and waived his rights.
Sigg, an Arapahoe Community College student, showed interest in mortuary and forensic science. Friends say he often wore black and hung out in the "goth corner" of the school's cafeteria.
One of Sigg's classmates said he had been bullied for having a high voice. Another friend of Sigg's says he wasn't a big fan of high school.
Childhood friend Elexus Parmitter knew Sigg very well.
"He was a like the outcast. He wasn't popular, he wasn't in any sports. He was just a really smart kid," she said. "I grew up with the kid. He has a great mom, his brother is very smart, his little brother. They're just all great."
CBS4 in Denver said Sigg came from a troubled home that included divorce and many run-ins with the police.
The CBS affiliate also said Sigg's father, Robert Sigg, has a long arrest history, including multiple DUIs, assault, domestic violence and drug-dealing arrests.
Robert Sigg was involved in numerous civil actions and was convicted in 2006 for involvement in a mortgage fraud scheme after he was arrested by the FBI, reports say.
Austin Sigg's mother also reportedly filed for Chapter 7 bankruptcy last May.
The arrest brought some relief to the community, which has been on edge as authorities searched for Jessica's killer. More parents have been waiting with their children at bus stops, and high school students have volunteered to walk younger children to school to keep them safe.
"Every parent in every Colorado community will rest a little easier tonight," said Gov. John Hickenlooper, who has a 10-year-old son. "While we still mourn the death of Jessica Ridgeway, we are relieved an arrest has been made and the pursuit of justice can continue."
Copyright 2012 KCTV (Meredith Corp.) All rights reserved. The Associated Press contributed to this report.
A Colorado girl went missing on Oct. 5. Her father, Jeremy Bryant, lives in Independence. He has traveled to Colorado to assist in the search for her. Independence family hopes for answers after AmberMore>>
Thursday, December 12 2013 10:51 PM EST2013-12-13 03:51:02 GMT
(WFAA/KTVT/CNN) - A Texas teenager killed four people while driving drunk and his attorney chose an unusual defense to keep him out of prison. Ethan Couch got drunk then jumped behind the wheel of hisMore >
A Texas teenager killed four people while driving drunk and his attorney chose an unusual defense to keep him out of prison.More >
Thursday, December 12 2013 8:12 PM EST2013-12-13 01:12:27 GMT
A 73-year-old woman who either fell or was ejected from her friend's car was subsequently struck by another car in Gresham late Wednesday night.Peggy Jennen, of Oregon City, died from her injuries. GreshamMore >
A 73-year-old woman who either fell or was ejected from her friend's car was subsequently struck by another car in Gresham late Wednesday night.More >
Wednesday, December 11 2013 8:51 PM EST2013-12-12 01:51:15 GMT
A parking dispute and a tube of lipstick led to criminal charges for a woman in Beaverton. Police said they were called to the Town Square Fred Meyer at 4:35 p.m. Dec. 3. A woman reported that a PorscheMore >
A woman reported that a Porsche SUV had parked extremely close to her Mercedes Benz, and when she made a statement to the other driver about it, an altercation ensued.More >
Defense attorneys say a Montana woman accused of killing her new husband won't testify in her defense.More >
A Montana newlywed pleaded guilty Thursday to killing her husband of eight days by pushing him from a cliff in Glacier National Park while they argued about her second thoughts about the marriage.More >
Thursday, December 12 2013 3:39 PM EST2013-12-12 20:39:19 GMT
A man walking in downtown Eugene was punched by a stranger who proclaimed, "knockout," after sending the victim to the ground. Police said it happened near the LTD bus station at 10th and Willamette atMore >
A man walking in downtown Eugene was punched by a stranger who proclaimed, "knockout," after sending the victim to the ground.More >
Wednesday, December 11 2013 4:28 PM EST2013-12-11 21:28:07 GMT
After reports that a baby was murdered at a Gladstone motel, the body of a 5-month-old child was found in a wooded area in Clackamas County. Police said the child's mother contacted officers at 5 p.m.More >
After reports that a baby was murdered at a Gladstone motel, the body of a 5-month-old child was found in a wooded area in Clackamas County.More >
Wednesday, December 11 2013 8:02 PM EST2013-12-12 01:02:46 GMT
A Salem woman will spend half as long in a federal prison as her husband, after they were both convicted of producing child pornography videos in their home. Michael Freeman pleaded guilty in August toMore >
Michelle Freeman was sentenced to 25 years in federal prison, a week after her husband was sentenced to 50 years for producing child pornography videos in their Salem home.More >