SAN DIEGO (AP) — Police raced Monday to catch an armed teenage runaway before he and another teen opened fire on a San Diego mosque, killing three men and then themselves.

About two hours after one teen's mother called to warn police that he had run away with her weapons and vehicle, shots rang out at the Islamic Center of San Diego, and a mosque security guard and two others were killed, San Diego Police Chief Scott Wahl said.

The gunmen, ages 17 and 18, were found dead of apparent self-inflicted gunshot wounds, the chief added.

The shooting is being investigated as a hate crime, he added.

Here's what is known about the attack:

Search for suspects began hours before attack

Wahl said the mother, who called the police around 9:40 a.m., had described her son as suicidal. The search for the teen took on more urgency as police learned that he was dressed in camouflage and with an acquaintance — facts that were not consistent with someone about to die by suicide, the chief said.

Police used automated license plate readers to try to find the teens, dispatched authorities to a nearby mall and alerted Madison High School, where at least one suspect was a student, Wahl said. Officers were still interviewing the mother about places the teens might be when they received reports of a shooting at the largest mosque in San Diego County.

WATCH: Teenage gunmen open fire on Islamic Center of San Diego, police say

As police arrived, gunshots rang out a few blocks away where a landscaper was shot at but uninjured. The shooters were soon found dead in a vehicle stopped in the middle of a road nearby, Wahl said.

Suspects engaged in 'generalized hate rhetoric'

There was no specific threat made against the Islamic Center of San Diego but authorities found evidence that the suspects engaged in "generalized hate rhetoric," Wahl said. He declined to immediately share more details.

The mosque's director, Imam Taha Hassane, said the center focused on interfaith relations, and that a group of non-Muslims had been touring the mosque earlier Monday to learn about Islam.

The white mosque is surrounded by homes, apartments and strip malls with Middle Eastern restaurants and markets. It is home to the Al Rashid School, which offers courses in Arabic language, Islamic studies and the Quran for students ages 5 and up, according to its website. No students were harmed, Hassane said, and aerial TV footage showed the school children holding hands as they were led out of the parking lot surrounded by police vehicles.

Security guard remembered as 'heroic'

Police have not yet released the names of the victims. But a family friend identified one as Amin Abdullah, a security guard whom Wahl said "played a pivotal role" in preventing the attack from being more deadly.

Shaykh Uthman Ibn Farooq said he had spoken with Abdullah's son. The family could not immediately be reached for comment.

"He wanted to defend the innocent so he decided to become a security guard," he said.

Wahl credited Abdullah with saving lives.

"It's fair to say his actions were heroic," the chief said at a news conference.