Police discovered the materials after John Zawahri threatened fellow high school students in 2006, Oscar de la Torre, a member of the Santa Monica-Malibu Unified school board, told The Associated Press.
The board was briefed by school administrators after police found Zawahri was learning to make explosives by downloading instructions from YouTube, 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."
The revelation came four days after authorities said Zawahri shot and killed five people during a 15-minute rampage that ended on a Southern California college campus as students were taking final exams.
Zawahri, 23, shot his father, Samir Zawahri, and his brother, Christopher Zawahri, on Friday, leaving their home in flames before shooting at strangers in cars and at Santa Monica College.
The former student at the school was heavily armed and carried a duffel bag with 1,300 rounds of ammunition before officers killed him in the campus library.
De la Torre, who was a neighbor 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," 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."
The victims also included Carlos Navarro Franco, 68, and his daughter Marcela Franco, 26. They were gunned down as he pulled his vehicle out of a parking lot at the college, where he worked as a landscaper and she was a student.
Also killed was Margarita Gomez, 68, of Santa Monica, a nonstudent who was shot outside the library.
Investigators were trying to determine whether problems in the Zawahri family played a role in the killings.
Zawahri's mother, Randa Abdou, said in court filings in 1998 that her husband threatened her and became abusive five years into their marriage when she moved from Lebanon to join him in the U.S.
Abdou also said her husband had threatened to take their two young sons to Canada after the couple separated at the time, and that he once punched her and stole her jewelry, purse and divorce papers she had started filling out.
Abdou has not spoken to the media.
Police say Zawahri had contact with officers in 2006 but wouldn't divulge details because he was a juvenile.
John Zawahri enrolled at Santa Monica College in the winter of 2009 and last attended in fall 2010, taking classes in the entertainment technology program, which involves video game design, animation and computer skills for digital media, the college said in a statement that also reported no disciplinary issues with Zawahri.
Neighbors have described Zawahri as reclusive and said his 55-year-old father was friendly though not overly social.
Zawahri's parents married in 1985, and in the mid-1990s his father brought his family to the Santa Monica neighborhood of small homes and apartment buildings tucked up against Interstate 10, according to property records. A neighbor said the couples had a difficult divorce and one son went to live with the father and the other with the mother.
Wendy Parise, who was a teacher at Lincoln Child Development Preschool and specializes in early childhood education, remembers 4-year-old John Zawahri as "very timid, withdrawn and very sensitive" while he was in her class.
In 1993, Zawahri's mother contacted the school terrified; not knowing where to go at the time. She told the school that "her husband had pulled a knife on her and her boys," Parise said. The school contacted a local battered women's shelter and Abdou went there.
When Parise saw a photo of John Zawahri identified as the Santa Monica gunman, she said she thought, "Ooh my God, I know this person, and it started to come back."
"I just picture him as a sad little boy who was not aggressive, very quiet, difficult to engage," Parise said. Zawahri wasn't social with the other kids, but Parise chalked that up to him being shy.
"Now I look back and I think he was traumatized as a child, he was living through all of that, and part of me thinks, what happened to this boy in subsequent years?" Parise said. "That family was poisoned and he lived in a poisonous environment, and that was devastating."
When Zawahri was 9, his now-separated mother sought a restraining order.
Abdou said her husband had "followed me, struck me, taken the children without telling me, and entered my apartment without my permission and removed photographs."
He once came to the apartment and told her that he was going to take the children to Canada, she said.
"The defendant said that he would do anything to make my life miserable and that he could kill me and no restraining order can stop him," she said.
She was afraid to press charges, she added, because he scared her and she didn't want to enrage him further.
Associated Press writers Christopher Weber, Anthony McCartney and Robert Jablon contributed to this story. Tami Abdollah can be reached at http://www.twitter.com/latams .
Copyright 2013 The Associated Press.