A person who lives across the street said that she saw a security guard outside the mosque in a tactical vest get hit by at least two gunshots. He fell, then stood up and went inside, she said.

Later, a landscaper was shot at from a vehicle a few blocks away from the Islamic Center. The bullet may have ricocheted against the helmet he was wearing, which likely saved his life, Chief Scott Wahl of the San Diego Police Department said.

A few minutes later, the police found a vehicle in the street with the two dead suspects inside. They appeared to have died from self-inflicted gunshots after opening fire at the mosque, Chief Wahl said.

Who are the victims?

Three people were killed in the shooting, according to a news release from the Partnership for New Americans, a community organization supporting the mosque:

• Amin Abdullah, a security guard;

• Mansour Kaziha, a store manager at the mosque;

• Nader Awad.

Mr. Abdullah, the partnership said in its release, “risked his own life to alert the school and other individuals” about the shooters, the organization said, adding “He is the definition of a hero.”

Mr. Kaziha was known as Abu Ezz and had managed the store at the mosque for nearly 40 years, the group said.

Mr. Awad, it added, “turned away community members from the bullets and saved lives.”

Who are the suspects?

The police said that the suspects were ages 17 and 18.

The police have not named either suspect. But two law enforcement officials with knowledge of the matter said the 17-year-old is Cain Clark and the 18-year-old is Caleb Vazquez, both of the San Diego area. The two officials were not authorized to speak publicly about the investigation.

Before the shooting, Mr. Clark’s mother reported to the police that her son was missing, and that he was suicidal said Chief Wahl, who did not refer to Mr. Clark or Mr. Vazquez by name. Also missing were several guns from her home, as well as her car.

The mother said Mr. Clark might be with a friend, Chief Wahl said. The police began a hunt for the two teenagers in San Diego, California’s second-largest city.

Investigators recovered anti-Islamic writing in the car where the suspects were found dead, according to the law enforcement officials. The words “hate speech” were written on one of the firearms used in the attack, they said, and one of the suspects left a suicide note.

James Canning, a spokesman for the San Diego Unified School District, who also confirmed that Mr. Clark was the 17-year-old suspect, said he had been set to graduate from this year from iHigh Virtual Academy, an online school within the district. He had not had any disciplinary infractions since elementary school.

Mr. Cain participated on the wrestling team at Madison High School last year but had not been involved in extracurricular activities this year, Mr. Canning said.

What is the Islamic Center of San Diego?

The Islamic Center of San Diego, in the city’s Clairemont neighborhood, is the largest mosque in San Diego County and draws attendees from all over the world. Its services are in English and its grounds include a school.

The mosque’s website says that its mission is to “work with the larger community to serve the less fortunate, to educate and to better our nation.” It holds prayers five times a day, as well as a Friday sermon.

The center said in a statement that it was “heartbroken by the tragic shooting incident,” calling it an “extremely painful and traumatic day for our congregation.”

Pooja Salhotra contributed reporting.