John Zawahri, who killed five people in a rampage in Santa Monica last week, apparently built his own assault weapon, using it to shoot his father and brother before he set fire to their family home, officials said today (NZ time).
Two officials who were briefed on the investigation said the semi-automatic weapon appears to have been built with component parts that are legal to obtain, but put together make the rifle illegal in California. They spoke on condition of anonymity because they were not authorised to speak publicly about the investigation.
The finding about the component parts was first reported by radio station KFI-AM.
The 23-year-old Zawahri's 15-minute midday rampage June 7 spanned a just over a kilometre between his father's home, where his father and brother were shot to death, and Santa Monica College, where police killed him in the library. Along the way, he fired at vehicles and strangers, fatally wounding three people. One other person was seriously wounded and two others had minor injuries.
Today (NZ time), an official close to the investigation said the fire at Zawahri's father's home, which erupted soon after neighbours heard shots fired, was intentionally set.
The official, who spoke on condition of anonymity because the information had not yet been publicly released, said the fires were started in a front living room and atop one of two twin beds in a room of the house.
Several boxes of matches were also found in the bedroom.
Firefighters found the bodies of the gunman's father and brother in a bedroom that was uninvolved in the blaze. The house was found unkempt with files and papers scattered throughout, providing ample kindling.
In Zawahri's bedroom, investigators found a drill press among other materials that indicate he likely assembled the weapon.
The drill press is used to help finish building the rifle by drilling holes in the lower receiver. A lower receiver that is only 80 per cent complete can easily be purchased, and because it is not complete, a person isn't required to go through a background check, nor does the part need to have a serial number.
In California such weapons require a "bullet button" kit, which needs to be added to a lower parts kit to make it legal. The bullet button kit modifies the weapon so that a separate tool must be used to release an ammunition magazine and reload the gun; without such a modification a person can press a button to release the magazine.
Zawahri was carrying 1300 rounds of ammunition in magazines that were capable of holding 30 rounds each. Such high-capacity magazines are illegal to purchase, sell or transfer in California. Possession is not illegal.
Zawahri's last reported contact with law enforcement was seven years ago, when bomb-making materials were found at his house during a search prompted by threats to students, teachers and campus police officers at Olympic High, a school for students with academic or disciplinary issues.
Retired police officer Cristina Coria, who helped serve the search warrant, said Zawahri was hospitalised for psychiatric evaluation at the time. She didn't know the outcome of the evaluation.
Police declined to provide further details, saying Zawahri was a minor at the time. But once a person is held for such an exam, they cannot access or possess firearms for five years.
In the case of Zawahri, that prohibition would have expired in 2011.
The Santa Monica-Malibu school board was briefed at the time by school administrators after police found Zawahri was learning to make explosives by downloading instructions from YouTube, school board member Oscar de la Torre said.