Authorities say 22-year-old Jacob Tyler Roberts shot and killed two people at a mall outside of Portland, Oregon, before turning the gun on himself Tuesday.

A day after the deadly incident, everyone was asking the obvious question: Why?

People who knew Roberts expressed disbelief that he was responsible for the brutal killings.

Erin Philpot, a friend of the shooter, said in an e-mail to CNN, "He was a very loved individual that always seemed as if he had great intentions and a heart of gold. I know that must be hard for people to see/think/understand, but it's the truth. I don't know what caused him to do such a horrendous, terrible thing, but I do hope that somehow answers will be available to us all."

Jordan Salazar, who attended Milwaukie High School in the Portland area with Roberts, said, "He was a really nice guy, and it's completely shocking he did this."

And Joe Krumm, the director of community relations for North Clackamas County School District, said Roberts had no record of discipline issues or extracurricular activities.

"He was known as a soft-spoken and polite young man who was often eager to be helpful,” Salazar said. “The motive for such a horrific act is likely to remain a mystery to us all."

Roberts though, who worked at a gyro eatery in Portland, wrote messages on his Facebook page like, “Hey what’s up guys my names Jake and I’m an alcoholic… Lol just kidding," and, “If you were to ask someone that knows me they would probably say that I am a pretty funny person that takes sarcasm to the max.”

On Wednesday night, HLN’s Dr. Drew and his guests took a closer look at the life of Jacob Tyler Roberts.

Watch the full segment in the video clip above.

Dr. Drew On Call airs Monday through Wednesday on HLN at 9 p.m. ET.  Follow the show on Facebook and Twitter @DrDrewHLN.

RELATED LINKS:

READ: 'Freaking out. Bad.' Oregon shooting, as it happened
READ: Victims, gunman ID'd in Oregon mall shooting
WATCH: Sheriff: 'Heartbreaking tragedy’ in Oregon

CNN Wires contributed to this report.