(This story last update at 4:00 p.m. ET)
Investigators in Santa Monica, Calif., were trying to piece together a motive in a shooting rampage in which four people were killed before police fatally shot the gunman.
The assailant, dressed in black and carrying a semi-automatic rifle, first shot and killed two men – believed to be his father and brother – at a home about a mile from Santa Monica College. Authorities were soon called to the burning home, but it wasn't immediately clear if the fire was arson.
Police say next the armed assailant carjacked a woman and ordered her to drive to the Santa Monica campus, where he shot at a bus, injuring three women. Authorities say their injuries were minor.
As he approached campus, the gunman fired on two people in an SUV. The vehicle crashed into a wall, killing the driver and seriously injuring the passenger, who doctors said was in critical condition after undergoing surgery, according to The Associated Press.
The gunman then exchanged fire with police before fatally shooting a woman outside the library.
Trena Johnson, a longtime administrative assistant working in the dean's office was quoted by the AP as saying she witnessed the library shooting. Looking out the window around noon on Friday, she described seeing a man with a "very large gun."
"We saw a woman get shot in the head," she said. "I haven't been able to stop shaking."
Police then exchanged gunfire with the suspect in the school's library, killing him.
Authorities say the gunman was carrying a canvas bag that included a rifle, a handgun and magazines of ammunition. A small cache of ammunition was also found at the house.
NPR's Sam Sanders reports that authorities have not identified the victims or the gunman, who they said was a white male in his 20s or 30s carrying an assault-style weapon.
Update at 4:00 p.m. ET. SUV Passenger's Prognosis 'Grim'; Suspect Had Attended College
Santa Monica Police Chief Jacqueline Seabrooks said the condition of the passenger in the red Ford Explorer is "grave" and that her prognosis is "grim."
Seabrooks, speaking at a Saturday news conference, said the suspect had been enrolled at Santa Monica College as recently as 2010.
She said his identity could not be released until next of kin were notified — they "may be out of the country," she said.
Seabrooks said police "had contact" with the suspect in 2006 but that he was a juvenile at the time, so she could not reveal details. She later said that Saturday would have been the suspect's 24th birthday.
The police chief says the gunman, who was armed with a .223 caliber semi-automatic "similar to an AR-15." tried to kill several people hiding in a safe room in the library and that it was "remarkable" that they were unhurt. She said the gunman was also wearing a "load-bearing vest" that was designed to take bullet-proof panels, but there were none in it.
She said the bag that he was carrying contained various clips and ammunition and that had he not been stopped, he could have fired some 1,300 rounds.
Update at 2:45 p.m. ET. Why The College?
The Los Angeles Times says police are trying to determine why the gunman wanted to go to the Santa Monica College campus.
The newspaper says the woman who was carjacked by the unidentified man, Laura Sisk, 41, said he specifically asked to be taken to the college.
"You're going to drive me to Santa Monica College and let me out," Sisk told the Times in an interview.
She said the man was dressed in black body armor and carried an AR-15 assault rifle.
Officials have been careful, however, not to characterize the rampage as a "school shooting" and to stress that while two people were killed on campus, the incident started elsewhere.
Update at 11:50 a.m. ET. Victim Identified
The driver of the vehicle who was killed has been identified as Carlos Navarro Franco, 68, according to police investigator, Joyce Kato.
Franco drove a red Ford Explorer that the gunman sprayed with bullets, killing him and wounding his passenger.