Austin Sigg's behavior seemed to become more emotional and confrontational about a year ago, say those close to the Jessica Ridgeway murder suspect.
Then the Colorado teen also became interested in crime scene investigation and bypassed his senior year of high school to study mortuary sciences in college.
Only recently did family and friends see these changes in a darker light.
Sigg in the October 5 kidnapping, sexual assault, murder, and dismemberment of Jessica Ridgeway, 10, an attack that horrified the Denver area and U.S.
"When I learned it was Austin, every single memory that gave insight to him doing it flashed into my head like a strobing movie," says Ash, 17, a close friend of Sigg's.
Authorities say they have DNA evidence and a Jessica Ridgeway's body parts under his mother's house., who reportedly directed police to
On October 30, he was charged as an adult with 17 counts involving the assault on Ridgeway and an attack on a 22-year-old jogger who got away.
But little has been offered so far to explain what may have driven Sigg to commit such a crime - not only to murder a child but also dismember the victim.
"He was completely harmless and non-threatening when I knew him," says classmate Joe Sanchez, 18, who spent time with Sigg and his girlfriend.
Other students picked on Sigg over his dark choices in clothing, his voice and his sometimes-abrasive personality, according to CBS4 in Denver.
Sigg dropped out in his junior year and got his GED so he could go to Arapahoe Community College "because he was pursuing his desire to be a mortician.
The school confirms Sigg is a student there, but says he hadn't yet taken enough classes to enter the mortuary sciences program. He was working on his GED.
He also attended nearby Warren Tech, where he showed an interest in forensic science and, in March, placed second in the CSI division of a statewide leadership conference.
Continue reading about his fascination with crime studies ...