John Samir Zawahri was born on June 8, 1989. He grew up in Santa Monica, California. His family included his father, Samir Zawahri, and his mother, Randa Abdou. He had an older brother named Christopher. In 1996, the family moved into a house on Yorkshire Avenue. Randa Abdou left the family home in 1998, taking her two sons with her. After this, she sought a restraining order against Samir Zawahri for domestic violence. However, the case was dismissed when she did not appear in court.

John attended Olympic High School in Santa Monica. In 2006, while he was a student there, a teacher noticed that he was searching for information about assault weapons and how to make explosive devices online. This raised concerns among school staff. They discovered that John had made threats against students and teachers. Soon after, police were called, and bomb-making materials were found at his home. Because of this, he was admitted to the UCLA Neuropsychiatric Institute.

After completing high school, John attended Santa Monica College in the winter of 2009. There were no reported disciplinary issues during his time at the college. However, he left the school in the fall of 2010.

On June 7, 2013, a series of violent events unfolded in Santa Monica, California. The California Highway Patrol received a report of gunshots fired at 11:52 a.m. When police arrived at a house on Yorkshire Avenue, they found the building on fire. After the fire was put out, two men were discovered dead inside from gunshot wounds. These victims were Zawahri's father, Samir, aged 55, and his brother, Christopher, aged 24.

After the fire and shootings at home, Zawahri, then 23 years old, armed himself with an AR-15-style semi-automatic rifle. He left his house and carjacked a woman driving a Mazda hatchback, holding her at gunpoint. A nearby driver tried to help the woman but was shot by Zawahri. He forced the carjacked driver to take him to the Santa Monica College campus.

While driving, Zawahri fired at a bus carrying multiple passengers, injuring three. When he reached the college, he shot into a vehicle, killing the operator, Carlos Navarro Franco, a 68-year-old groundskeeper, and fatally wounding his passenger, Marcela Diaz Franco, who was 26. Outside the college library, he shot another woman, Margarita Gomez, aged 68.

Zawahri entered the college library and fired at students inside. He targeted a group of library employees who were hiding. Witnesses reported hearing many gunshots and screams. While on campus, he fired a total of at least 70 rounds and dropped a bag containing ammunition and a revolver.

Police arrived quickly and exchanged gunfire with Zawahri in the library. He was shot by the responding officers and succumbed to his injuries outside the building. Autopsy reports later revealed that he had received 25 gunshot wounds.

In total, six people died as a result of this violent spree, including Zawahri himself. One more victim, Marcela Diaz Franco, died two days later from her injuries. Four additional people were injured during the incidents, receiving treatment at a local hospital.

The shooting led to immediate lockdowns at Santa Monica College and surrounding schools. Mental health support was provided for students and staff in the aftermath. The tragic events raised concerns about gun violence, leading to changes in firearm policies on college campuses in California.