Ali Syed was a 20-year-old loner who took occasional computer classes at a community college and spent a lot of time alone in his room playing video games, said an Orange County Sheriff's Department spokesman.
How he crossed paths with 20-year-old Courtney Aoki remains a mystery.
Early Tuesday morning, Aoki was in Syed's bedroom, inside the town house he shared with his parents in the upscale Ladera Ranch development. Gunshots rang out from the bedroom, and Syed ran out of the house and drove away, police said. Aoki was dead from multiple wounds from a shotgun Syed's father had bought him about a year ago.
So began a rampage through Orange County in which Syed killed three people and injured three others before taking his own life, police said.
Authorities on Wednesday released 911 tapes in which Syed's frantic parents reported the shooting.
But officials said they were no closer to knowing a motive for the shooting rampage.
"There's still a lot of work to do in this case," sheriff's spokesman Jim Amormino said.
Syed left "no evidence, no note, no nothing that would explain this very bizarre, violent behavior."
Authorities said they didn't know how Aoki got to the Ladera Ranch home. She was dressed when she was found, and there was no evidence of sexual assault.
Syed's mother called 911 at 4:45 a.m. Tuesday.
"I think somebody's shot ... in my house," she said. "Somebody's shot. I think there's somebody shot."
Hysterical, the woman tried to answer the dispatcher's questions. Her husband eventually took over the phone.
"Can you please send somebody here?" he said. "Our son lives with us and I think they got into a fight or something and we heard a gunshot."
The parents told the 911 operator that they were sleeping when they heard what they thought was a gunshot downstairs. They did not enter their son's room, they told a dispatcher, but said he had left the home in their SUV.
"He's gone out," the father said. "He took the car we have.... Yes, he's not home right now. He drove away."
They told the dispatcher they did not see a victim.
"I have not gone in his room," the father said in answer to a dispatcher's questions. "I don't know what's going on."
Detectives had difficulty identifying Aoki, Amormino said, because she had no identification and no vehicle at the Ladera Ranch residence.
No missing person reports had been filed on her.
Amormino said Aoki was identified Wednesday morning from a second set of fingerprints, but authorities were unable to find her mother until about 2:30 p.m. Although Aoki's mother also lives in Orange County, Aoki did not live with her, Amormino said.