( CNN ) -- His stare stayed with them for days . The cold , harsh way he looked at them . The unease they just could n't shake off when he did . So , when Austin Reed Sigg was arrested Tuesday night , accused of strangling 10-year-old Jessica Ridgeway , dismembering her and placing her body parts under the two-story home where he lived , many of the girls in that Denver suburb were n't shocked . `` He was so infatuated with the idea of death , '' Hannah Bane , a college classmate , told a local reporter . Detectives spent a bitter-cold Wednesday at Sigg 's home in Westminster as crime scene technicians gathered more evidence in the gruesome case . They said they found parts of Jessica 's body stuffed in a crawlspace under the home . The bespectacled blonde girl disappeared October 5 while walking to Witt Elementary School . Five days later , police first found parts of her body at a park 5 miles away . Volunteers formed search parties and continued scouring . The big break came Tuesday night , when Sigg 's mother called 911 and handed him the phone . Sigg , police said , confessed . The arrest shocked many in the city , known for its interconnected walking trails and lush open spaces . But Christie Mueller was n't one of them . She had bumped into Sigg , 17 , twice on an isolated trail in the city . And both encounters startled her . Sigg was with friends , and the way he stared at her made her fear for her safety , she said . `` It just really freaked me out , '' Mueller told a local reporter . She said she brought her dog with her on the trail , a rugged-looking pit bull . `` I think if he had n't been with me that day , I just wonder what would have happened . '' Those who know him say Sigg was into forensics . He won awards in student crime scene investigation competitions . His father , on the other hand , had a history of committing them . The father had been arrested many times , local television stations said -- accused of domestic violence , assault , bank fraud . Sigg 's parents are divorced . The local district attorney said Sigg , a student at Arapahoe Community College , will be tried as an adult . His first court appearance is set for Thursday . 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 . One woman shocked by all of this was Sigg 's ex-girlfriend , who spoke to a local reporter but only under an assumed name . `` The Austin I knew would never have done anything like that . He was my first boyfriend . He was my first kiss . He was my first date , '' said Danni . `` He was so sweet and so kind . I know that heart is still in him . '' But in his neighborhood , Sigg was known more for his penetrating stare . It was so cold , Emily Alexander said , that it bothered her daughter for days . `` She was freaked out by a teenager staring at her at the park , '' Alexander said . `` After Jessica was kidnapped , she told me she knew who it was . `` She was sure she knew who it was , and it was this teenager . Because he was 17 . I did n't believe her . '' Now her daughter , like many in the neighborhood , find themselves once again facing that stare -- from Sigg 's mugshot as it blares from television newscasts . And , once again , feeling uneasy . This story was written by Lateef Mungin with reporting from CNN and its affiliates KMGH , KCNC , KUSA and KWGN .
Austin Reed Sigg was arrested Tuesday night . He is accused of killing 10-year-old Jessica Ridgeway . Police say he confessed and part of the girl 's body was found at his house . He has his first court appearance on Thurdsay .