One of the San Diego mosque shooters left a hate-filled suicide note 'about racial pride' before opening fire and killing three people, authorities say. Cain Clark, 17, attacked the Islamic Center of San Diego alongside Caleb Vazquez, 18, around 11.40am on Monday, after apparently stealing guns and a car from his home. Hours before the attack, Clark's mother reported to police that her son was suicidal and potentially armed with weapons, and officers were already searching for the teenager when he opened fire. After killing three, the teenagers were found in a car near the mosque with self-inflicted gunshot wounds. Police said one of the weapons in their vehicle had 'hate speech' written on it, sources told the LA Times. Sources told the outlet that when officers searched Clark's home around two miles from the mosque, they discovered a suicide note 'writing about racial pride.' A gas canister emblazoned with a Nazi SS sticker on its side was seen next to the BMW X1, where the suspects were found dead, with a shotgun nearby.Clark was enrolled in a virtual learning academy at the San Diego Unified School District and was set to graduate from high school this semester, officials said. He was previously a star wrestler at Madison High School, but had only been attending classes online for some time, as officials said he had spiraled into 'hate speech.' Clark's grandparents, David and Deborah Clark, told CNN they have been left stunned and heartbroken by the tragedy, saying they were 'trying to process this' and were 'very sorry for what happened.' Cain Clark, 17, was one of two suspects who opened fire at a California mosque on Monday before taking his own life. The other, Caleb Vazquez, 18, has not yet been pictured Images from the scene where the teenagers were found dead showed a red gasoline canister with a sticker resembling a Nazi SS logo, as a shotgun lay nearbySan Diego police said on Monday that hours before the tragedy, his department got a call from the teenager's mom, who was concerned he was suicidal. The parent, who has not been named, said she realized several of her guns were missing, and said she saw him and a companion wearing 'camouflage outfits', Chief Scott Wahl said. He added that although Clark's mother warned cops that her weapons were missing, she did not indicate any kind of planned attack on the mosque. 'There was no specific threat, especially no specific threat to the Islamic Center,' the police chief said. 'It was just general hate kind of speech that I think covered a wide gamut.' Police said they arrived at the Islamic Center within minutes of the shooting and found three people deceased in front of the building, including security guard Amin Abdullah, who was hailed as a hero as he saved lives during the chaos. Several blocks away, a landscaper was also shot at but was not hit, and minutes later, police received a call about shots being fired down the street. Clark and Vazquez were found dead inside a vehicle on Salerno Street, several streets away from the Islamic Center. While authorities and police sources have revealed some details of Clark, little is known about Vazquez. Amin Abdullah, a father of eight, was among those killed in the rampage