Investigators tried to piece together a confusing string of incidents involving a gunman who killed four people in a rampage through Santa Monica, that ended when police fatally shot him at a junior high school library where pupils had been studying for exams.
It was not clear what may have spurred the rampage.
For hours the California campus remained on lockdown as police methodically searched buildings for additional victims and possible other suspects.
Later, a Santa Monica police official said investigators believed the gunman had acted alone. The official also said that a "person of interest" taken into custody had been cleared of any involvement.
The events unfolded about noon along Pico Boulevard and on the campus of Santa Monica College. The first signs of trouble came about 11.50am, when gunshots rang out at Kansas and Yorkshire avenues, a quiet neighbourhood nestled along the Santa Monica Freeway.
Jerry Cunningham-Rathner had watched her son walk out the front door of her home a few minutes earlier and rushed outside, fearing he had been shot.
Instead, looking across the street, she saw a house in flames. A man standing in front of the house was dressed in black, with an ammunition belt around his waist and a large rifle in his hands. "He looked like a SWAT officer," she recalled later.
Firefighters would later find the bodies of two men inside the house. Police sources said the men were Samir Zawahri, 55, the owner of the house, and one of his adult sons. A second son was suspected of being the shooter, the sources said.
Cunningham-Rathner looked on 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 US President Barack Obama was in town for an event a few kilometres away and thought momentarily the man might be a Secret Service agent. She quickly realised 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 responded.
Before sitting next to Sisk, he fired several shots aimlessly around the neighbourhood with what authorities later said was an "AR-15 style" semi-automatic rifle, according to witnesses.
Other than telling her where to turn, the man said little during the short drive down Pico Boulevard towards 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 strafed the outside of a bus from front to back, shattering the windows. Passengers threw themselves to the floor for cover.
After shooting at the bus, Sisk recalled the gunman shouting at her to "Go! Go! Go!"
"So I drove, drove, drove," she said. They continued towards the campus. At a school car park 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 stop and let him out. After he got out, 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 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 towards the school's library and shot a woman outside the building's entrance.
The woman outside the library later died of her injuries at a hospital. During the rampage, five others were wounded, two seriously, police said.
The library was filled with pupils 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 pupils ran from the building or hid in rooms and under tables.
Officers then shot the man. They carried him outside, where he died on a footpath.
The investigation led police to an apartment on south Centinela Avenue in Los Angeles, where the shooter was believed to have lived with his mother.