The man, identified by police as John Earnest, was detained near the synagogue Chabad of Poway and St. John of Damascus Orthodox Church.
At a press conference, officials said an older female died but that the three other victims, including one young girl, are in stable condition.
After shooting inside the temple with an AR-type assault weapon, the suspect was spotted by a Border Patrol agent who opened fire on the teen but missed, officials said. The suspect later turned himself over to police.
The synagogue was hosting its Passover holiday celebration, which was scheduled to begin at 11 a.m., just a half hour before the shooting incident. 10News reported. The celebration was set to end at 7 p.m. with a final Passover meal.
Earnest posted an 8-page manifesto online prior to the attack. In it, the suspect gloats about being from “European ancestry” and expresses his hatred of Jewish people. He says he feels “no remorse” for his upcoming actions that would leave one person dead, and that he took inspiration from the New Zealand mosque shooter that left more than 50 dead in March. Earnest also appeared to be a frequent user of racist gutter forum 8chan, and mentioned his desire for “the day of the rope,” a far-right term about a desire to kill journalists.