The FBI joined local authorities on Saturday in seeking to determine a motive for a gunman's rampage that killed four people in Santa Monica.
The gunman, who was also fatally shot by police to end Friday's harrowing incident, has not been identified. But law enforcement sources said his first victims were his father and brother, whose bodies were found in a burning home.
The sources said they believe those deaths appeared to be tied to a family dispute. But they stressed the investigation is still in its early stages.
Authorities said detectives were trying to look into the background of the alleged gunman as well as his family. They also want to know how he got the semiautomatic rifle he used.
Police are expected to hold a news conference Saturday morning.
The first signs of trouble came about 11:50 a.m. Friday, when gunshots rang out in the vicinity of Kansas and Yorkshire avenues, a quiet neighborhood nestled along the Santa Monica Freeway.
Jerry Cunningham-Rathner had just watched her son walk out the front door of her home a few minutes earlier when she heard the shots. She rushed outside, fearing he had been hit.
Instead, looking across the street, she saw a house engulfed in flames. A man standing in front of the house was dressed all in black, with an ammunition belt around his waist and a large rifle in his hands, she said.
"He looked like a SWAT officer," she said.
Firefighters later found the bodies of two men inside the house. Police sources, who requested anonymity because of the ongoing investigation, said the men were Samir Zawahri, 55, the owner of the house, and one of his adult sons. A second son is suspected of being the shooter, the sources said.
Cunningham-Rathner looked on in horror as two cars approached. The man pointed his weapon at the first, a Mazda hatchback, and yelled at the driver to stop. Cunningham-Rathner said he motioned for the woman driving the second car to keep moving. When she hesitated, the man opened fire on her silver Infiniti, wounding the driver slightly.
Laura Sisk, 41, the driver in the first car, froze, she later said. She knew President Obama was in town for an event a few miles away and thought momentarily the man might be a Secret Service agent. She quickly realized that wasn't the case.
"You're going to drive me to Santa Monica College and let me out," she recalled the gunman saying.
She begged him to take the car instead. "No. You're driving," he said.
Before getting into the passenger's seat next to Sisk, witnesses said, the gunman fired several shots aimlessly around the neighborhood with what authorities later said was an "AR-15 style" semiautomatic rifle.
Other than telling her where to turn, the man said little during the mile drive down Pico Boulevard toward the college campus, Sisk said. He was calm, she said.
Sisk said she was crying and shaking as she drove. The gunman reassured her. "He told me to calm down," she said. "He said he'd let me go if I didn't do anything stupid."
Near Cloverfield and Pico boulevards, the gunman fired at the outside of a public bus from front to back, shattering the windows. Passengers dived to the floor for cover, said Marta Fagerstroem, a student from Sweden, who was on the bus and studying for an exam.
A woman sitting in the back row was grazed in the head by a bullet, witnesses said.
"It happened so fast," said Fagerstroem, her voice quavering. "You don't expect this."
Sisk said that after shooting at the bus, the gunman shouted at her to " 'Go! Go! Go!' So I drove, drove, drove."
They continued toward the campus. At a school parking lot at 20th and Pearl streets, the shooter opened fire on two people in a Ford Explorer, police said. The driver died at the scene, and the passenger was badly wounded. Shortly after, Sisk said, the man ordered her to let him out. After he exited, she sped down the block and then got out of her car and ran.
By that time, officers from the Santa Monica Police Department and the college's police force had received numerous 911 calls reporting the chaos.
The calls took on an even sharper edge with the president in town attending an event at the same time nearby. Federal authorities were quickly made aware of the situation.
Campus police intercepted the gunman on the edge of campus and exchanged gunfire with him, authorities said. They continued to trade shots as the man ran toward the school's library and shot a woman outside the building's entrance before disappearing inside.
The woman outside the library later died at a hospital.
During the rampage, five people were wounded, two seriously, police said.
The library was filled with students studying for year-end exams and the gunman "accosted" several of them, Santa Monica Police Chief Jacqueline Seabrooks said, as he unleashed another barrage of bullets. Hearing the shots, panicked students ran from the building or hid in rooms and under tables.