LOS ANGELES - A gunman who killed five people in Santa Monica, California, last week was hospitalised for psychiatric evaluation in 2006 after police found bomb-making materials at his home.

Police searched the house where John Zawahri lived with his father after the teen made repeated violent threats against students, teachers and campus security officers at Olympic High School, retired police officer Cristina Coria, who helped execute the search warrant, said on Tuesday.

Ms Coria said she did not know what was found at the house or the outcome of that mental evaluation.

Mr Oscar de la Torre, a member of the Santa Monica-Malibu Unified school board said that police had discovered bomb-making materials at the home.

The school board was briefed by school administrators after police found Zawahri was learning to make explosives by downloading instructions from YouTube, Mr de la Torre said.

"It was some type of devices or materials that would be able to make explosives, and the word 'pipe bombs' was what was referred to," he said. "If it was guns and stuff like that, it would have been more serious, but because it was explosives, it wasn't deemed 'Oh my God', just that this guy had a fascination."

Investigators are looking at Zawahri's police history, along with a stormy family life, to determine what led to the chaotic shooting on Friday on a Southern California college campus.

That encounter seven years ago appeared to be the last reported run-in Zawahri had with police until he died in a shootout with officers on Friday.

Santa Monica Police Sergeant Richard Lewis said a pipe was found in the home, but declined to provide more details because Zawahri was a juvenile at the time.

Zawahri was not expelled, but he did not finish classes at Olympic High - a school for students who have academic or disciplinary issues.

District superintendent Sandra Lyon said that Zawahri attended the school for six months during 2006.

Zawahri, 23, shot his father Samir Zawahri, 55, and his brother Christopher Zawahri, 25, on Friday, leaving their home in flames before shooting at strangers in cars and at Santa Monica College, in a 15-minute rampage that occurred as students were taking final exams and ended with John Zawahri fatally shot by officers in the college library.

The victims included a campus groundskeeper and his daughter, who was a student at the college, and a woman collecting cans outside the library.

Graduation was held on Tuesday at the college where jittery students returned on Monday. Commencement ceremonies were punctuated by a moment of silence as graduates and their families, along with administrators and faculty, stood and paused on the campus football field.

"We have come together as a community to heal and to pay homage to the victims," said the school's president Chui L. Tsang, according to City News Service.

Many questions remained for returning students as investigators examined how Zawahri had access to an assault-style rifle, an old revolver and 1,300 rounds of ammunition that he had carried with him.

Mr De la Torre, who was a neighbour of Zawahri, said the gunman's father told him he was having problems with his son eight months ago.

"They didn't talk to a lot of people, they were very reserved," Mr de la Torre said. "One time he did tell me he had problems with his younger son, knowing I work with youth. He never went into detail about anything." Zawahri took classes in video game design, animation, and other technology-related subjects at Santa Monica College in 2009 and 2010. He had no disciplinary issues at the school.

Ms Coria was a campus resource officer teaching a seminar on bullying and reporting threats in 2006 when she first took notice of Zawahri sitting at the back of a classroom.

"I remember him specifically because he had the long hair," Ms Coria said. "He had the black outfit on, the black trench coat, the black boots. He was very thin. He just had that isolated look."

She said another campus officer warned her afterwards to keep an eye on Zawahri because he had been taken in by campus police for making threats.

A teacher saw "disturbing behaviour, conversations around weapons and violence," said district superintendent Sandra Lyon.

Zawahri was held by a hospital for psychiatric evaluation after the search of his home, Ms Coria said. 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.

Investigators were trying to determine whether problems in the Zawahri family played a role in the killings.

Zawahri's mother Randa Abdou said in a 1998 court filing seeking a restraining order that her husband had threatened to kill her twice and became abusive five years into their marriage after she had moved from Lebanon to join him in the United States.