"It's truly scary to know that [he is] one of my fellow students and classmates," Justin Gunn, s student at Arapahoe Community College, said. 

Sources tell 9NEWS that Sigg showed interest in the school's mortuary sciences. ACC is the only accredited mortuary-science program in the state of Colorado and develops future funeral directors and morticians.

Gunn says Sigg's arrest was addressed in his finance class.

"Instantly, our teacher was obviously very curious about it," Gunn said. "So, instantly we did some research, looked it up, got in some good conversation about it. People are worried. People are scared. You know, you never know. It's a terrible situation."

Before attending college, Sigg spent most of his school career in Jefferson County. He attended Witt Elementary, the same school as the murder victim, 10-year-old Jessica Ridgeway. Sigg spent a few years at Standley Lake High School. 

He also concurrently attended WarrenTech, a trade school. 

According to Jeffco School District records, Sigg dropped of both schools in July 2012.

Around his neighborhood, residents are in disbelief.

"It's just terrifying to think that something is so close to home. You know, we want to raise a child and have a safe neighborhood. And, I don't even want to go outside right now," Lexi Thornton, who lives down the street from Sigg, said. "You can't let it rule your life, but for the time being you have to."

Thornton says she saw Sigg around the neighborhood, but never talked with him.

"It's sad for both parties involved -- the parents of this boy and the parents of Jessica Ridgeway," Thornton said. "I mean, what do you do? You have no control. It's just, it's heartbreaking."

(KUSA-TV © 2012 Multimedia Holdings Corporation)