The attack at the Islamic Center of San Diego is being investigated as a hate crime, San Diego Police Chief Scott Wahl said at a news conference at a neighborhood park across from the mosque.
WATCH: San Diego police chief provides update on shooting
Mom of SD gunman alerted police that son was a runaway, weapons were missing
Three men, including a security guard identified as Amin Abdullah, were killed in the shooting.
Both suspects, ages 17 and 18, are dead from apparent self-inflicted gunshot wounds, police said. Authorities initially said one of the suspects was 19, before later updating the age.
Police chief shares timeline, new details on suspect
The shooting at the Islamic Center of San Diego was reported shortly before noon Monday, police said.
About two hours before the attack, Wahl said a mother reported her teenage son was suicidal and had run away. She also reported her weapons were missing, along with her vehicle.
The mother also found a note, Wahl said, the contents of which the police chief did not share.
The mother told police that her son was with another individual and that they were both "dressed in camo," Wahl said.
Officers began using whatever technology they had available to locate the teens, including automated license plate readers.
Officers were attempting to track down the vehicle and dispatched police to a mall and to a school with which one of the teens was associated.
Wahl said that's when police began getting reports of a shooting at the Islamic Center of San Diego.
Responding officers found the three victims at the mosque and the two teens dead of apparently self-inflicted gunshot wounds in a vehicle nearby.
There had been no specific threat made against the Islamic Center of San Diego, but Wahl said investigators were aware of "generalized hate rhetoric" in the case and are investigating the attack as a hate crime.
Police have not released the names of the teenagers.
On Monday night, heavily armed FBI agents were seen entering the home of one of the suspects. They were seen with guns drawn as they approached the door.
ABC News and the Associated Press contributed to this report.