Yahoo News reports
Investigators trying to determine why Zawahri planned the shooting spree focused on a deadly act of domestic violence that touched off the mayhem.
Police said he fatally shot his father and older brother at a home that went up in flames before taking the violence to the streets, which lasted just a matter of minutes until he was shot to death in a chaotic scene at the Santa Monica College library by police.
Authorities did not immediately name the shooter or the two men found dead in the house because next of kin was out of the country and hadn't been notified. That changed Sunday after Zawahri's mother cut her trip short and came back to the country.
Sgt. Richard Lewis, a police spokesman, said she was being interviewed by investigators, who were hoping she could help provide clues about what triggered the violence.
"A big piece of the puzzle just came home," he said.
The killing began as a domestic violence incident when Zawahri killed his father, Samir, 55, and brother, Christopher, 24, in their home near Interstate 10 in a working-class part of town a few miles from the beachside attractions that draw tourists year-round.
The gunman, carrying a duffel back with him with 1,300 rounds of ammo, set the house ablaze, fired shots in the neighborhood and took his rampage on the road.