Muslim community leaders and police are looking at ways to increase security around mosques and Islamic schools across California after a deadly shooting Monday at the Islamic Center of San Diego.

The shooting killed three people and wounded a gardener. Two teenage suspects were found dead from apparent self-inflicted gunshot wounds in a car nearby.

Zahra Billoo, executive director of the Council on American Islamic Relations in San Francisco, said the crime is horrifying.

“This is the biggest mosque in San Diego County, and school was in session,” Billoo pointed out. “So many Muslims I know either knew someone there or knew someone who had someone there.”

Billoo pointed out the Muslim community has been fearful for several years following the war in Gaza and now the war in Iran.

The U.S. has seen multiple high-profile anti-Muslim acts of violence recently. In March, a man fired a pellet or paintball gun at children near the Islamic Center of North Phoenix. In December, a man attacked Muslim women with a metal rod as they left a community center in Fairfax, Virginia. Last year, someone set fire to two Islamic centers in Minneapolis.

Billoo is confident San Diego authorities will get to the bottom of the latest violence.

“The story is so horrifying,” she stressed. “Attacking a mosque, attacking a school, and then learning that these were teenagers. None of it makes any sense, and it's going to be important that we let law enforcement do their job and thoroughly investigate what happened.”

The Islamic Center of San Diego has been through difficult times before. In 2016, supporters of President Donald Trump and counterprotesters rallied across the street from the site after Trump tried to ban entry into the U.S. by people from several majority-Muslim nations.

Before Monday’s shooting, the Gun Violence Archive had recorded 150 mass shootings in the United States this year alone.