(CNN) -- His stare stayed with them for days.

The cold, harsh way he looked at them. The unease they just couldn'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 weren'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 crawl space under the home.

The bespectacled, blond little girl disappeared Oct. 5 while walking to Witt Elementary School.

Five days later, police first found parts of her body at a park five 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 wasn'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 hadn'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 didn'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.

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