His actions had undoubtedly delayed, distracted and ultimately deterred the two suspects from reaching the area of the mosque where up to 140 children were located, San Diego Police Chief Scott Wahl told a press conference on Tuesday.
According to Wahl, the security guard exchanged fire with the 17- and 18-year-old attackers.
During the exchange, he was seen using his radio to order the building to be locked down.
"Tragically, he died in that gun battle," Wahl said.
According to current findings, the two other people killed also tried to draw the attackers' attention away from the mosque and towards a car park. Wahl said the two men were cornered and killed by the attackers there.
If the suspects had not been diverted from their plan, "without question, there would have been many more fatalities yesterday", Wahl said.
The imminent arrival of police eventually forced the attackers to flee, he added.
Police are investigating Monday's attack as a hate crime after investigators found anti-Islamic writings in the suspects' vehicle and hate messages on one of the weapons used.
Three people were killed in the attack. The two suspected shooters were later found dead in a car, apparently from self-inflicted gunshot wounds.
Wahl said further evidence had been secured during searches, including 30 firearms and a crossbow.
The teenagers were radicalised online where they first met and shared white supremacist views, according to authorities and writings they authored.
The pair "didn't discriminate on who they hated," Mark Remily, the lead FBI agent in San Diego, said on Tuesday.
The writings, obtained by The Associated Press, include hateful rhetoric toward Jewish people, Muslims and Islam, as well as the LGBTQ+ community, black people, women, and both the political left and right.
Both express beliefs that white people are being eliminated, and one writes about mental health struggles and being rejected by women.
with AP
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