Earnest is associated with the Alt-Right movement.
Earnest was a 2017 graduate of Mt. Carmel High School and a nursing school student at California State University San Marcos (CSUSM). Officials said he had no previous criminal record or contacts with police, and no known connection to any white supremacist group. The shooter apparently attempted to livestream the shooting on Facebook, but failed.
In an antisemitic and racist open letter posted on 8chan shortly before the shooting and signed with Earnest's name, the author blamed Jews for the supposed white genocide conspiracy theory, which he referred to as the "meticulously planned genocide of the European race". He cited shooters Brenton Tarrant and Robert Bowers for their involvement in respectively the Christchurch shootings at Al Noor Mosque and Linwood Islamic Centre in Christchurch, New Zealand and the Pittsburgh synagogue shooting at Tree of Life - Or L'Simcha Congregation in Pittsburgh, Pennsylvania, as well as Jesus Christ, Paul the Apostle, Martin Luther, Adolf Hitler, Ludwig van Beethoven, Moon Man and Pink Guy for being the figures who inspired him to commit the Poway shooting as well as a joking mention of PewDiePie and referencing "The Day of the Rope" an event from William Luther Pierce's neo-Nazi novel The Turner Diaries (1978) in which Jews, non-whites and liberals are executed including racial slurs targeting African-Americans and Hispanics and urged more violent attacks while avoiding arrest.
He condemned President Donald Trump as a pro-Zionist traitor. He also justified his actions by including Bible quotes in his manifesto. The author also claimed responsibility for a March 2019 arson attack on a mosque in Escondido, California, about 15 miles (24 km) from Poway. That arson attempt was extinguished with only minor damage to the building and no injuries; graffiti left in the parking lot made reference to the earlier Christchurch shooting.
Earnest was a member of the Escondido Orthodox Presbyterian Church, which is affiliated with the theologically traditionalist Orthodox Presbyterian Church. According to The Washington Post, the shooter's manifesto, which expressed Christian motivations for killing Jews, led to a social media debate among Christian pastors. Rev. Duke Kwon of the Presbyterian Church in America said that the manifesto contains "a frighteningly clear articulation of Christian theology" on certain issues such as salvation, and warned that "There’s a deep and ugly history of anti-Semitism that’s crept into the Christian church, that needs to be continuously addressed, condemned and corrected." Other ministers strongly denied that Christian theology and scripture offer any support for anti-Semitism. The Orthodox Presbyterian Church issued a statement that "[a]nti-Semitism and racist hatred which apparently motivated the shooter . . . have no place within our system of doctrine." In the alleged shooter's manifesto, he denied that he had learned anti-Semitic beliefs from his family.
At approximately 11:23 a.m. PDT, Earnest entered the Chabad of Poway synagogue on the last day of the Jewish holiday of Passover, which fell on a Shabbat. Approximately 100 people were inside the synagogue. The gunman carried a Smith & Wesson Model M&P 15 Sport II semiautomatic rifle and was wearing a tactical vest which contained five magazines of ten rounds each. In the foyer, Earnest shot and killed 60-year-old Lori Gilbert-Kaye, and then wounded Rabbi Yisroel Goldstein, the founding rabbi of the congregation. According to witnesses, Gilbert-Kaye had tried to shield the rabbi from the gunman. Earnest then turned to a side room occupied by several people, including a number of children. He fired into the room, wounding one man with a bullet to the leg. The man's 8-year-old niece was also injured by bullet fragments that hit her face and leg. All the injured are expected to recover, although Goldstein lost his right index finger despite four hours of surgery. After Earnest fled, Goldstein spoke to the congregation despite his injury, telling them to stay strong.
Earnest fired eight to ten rounds before his rifle jammed or malfunctioned, preventing additional casualties. Two members of the congregation ran towards him. He then fled the synagogue, entering a Honda sedan. An off-duty United States Border Patrol who was a member of the synagogue, opened fire as Earnest escaped and hit his car multiple times, but he fled uninjured.
Shortly thereafter, Earnest phoned 911 and reported the shooting. He was apprehended approximately 2 mi (3.2 km) from the synagogue by a San Diego police officer responding to the shooting. Earnest jumped out of his car with his hands up, and was taken into custody without incident. The rifle, a tactical helmet, and five loaded magazines with 50 rounds, were recovered from Earnest's car; Earnest was wearing a tactical vest when he was arrested.
Surveillance cameras at the synagogue captured video of the shooting. The attack occurred exactly six months after the Pittsburgh synagogue shooting.