"I think something in his mind clicked and it messed with his thinking and he just wasn't himself anymore," said Roberts' friend, Yelena Voznyuk.
The 22-year-old's friends and even his ex-girlfriend are baffled. Hannah Sansburn tells ABC News that Roberts quit his job and sold all his belongings, telling her he was leaving Portland and moving to Hawaii.
"And this is the last thing I would ever expected, especially from him," ex-girlfriend Hanna Sansburn said. "He was just too sweet. Never mean to anybody, ever. Everybody loved him."
Roberts' victims were also well loved. Friends and relatives say 54-year-old Cindy Ann Yuille and 45-year-old Steven Forsyth were both caring parents and role models.
The third shooting victim, 15-year-old Kristina Shevchenko, was shot in the chest and survived. She is in a serious condition right now, but is expected to recover.
"It's clear to me she's a very brave young woman," said Dr. Laszlo Kiraly with Oregon Health & Science University.
Police say Roberts stole an AR-15 semi-automatic rifle from someone he knew and wore a ballistic vest and white hockey mask during Tuesday's shooting spree.
Robert's mother had a family friend read a statement. She says she "has no understanding or explanation" for her son's behavior.
There is concern over possible copy-cat shootings. Portland-area police are increasing patrols at malls and shopping centers.
Authorities say they don't yet have a motive for the attack