SAN BERNARDINO, Calif.- The terrorist attack has left this community rattled and fearful. A routine mall burglary in neighboring Riverside earlier this week set off a social-media-enhanced rumor of another mass shooting. In just half an hour, 350 people called police in a panic.

The post-massacre atmosphere has also provoked anxiety among Muslims in this part of Southern California. On Friday, an arsonist started a fire with a Molotov cocktail in a lobby of a mosque in the desert town of Coachella. And in Redlands, someone with a Sharpie wrote “F--- Muslims” on the boarded-up exterior of the apartment where the husband and wife terrorists had lived.

Yousuf Bhaghani, the president of the board of a mosque in the city of Corona, said that almost every night, someone drives by and shouts hateful messages – such as “Go home, terrorists!”

At the same time, there have been efforts at healing. That included a gathering Friday night in which 650 people from a variety of religious faiths gathered at that same mosque and heard speakers condemn bigotry, racism and extremism. Muslims spoke of their pride in being Americans and their dismay at the violence carried out by terrorists.

“We have always made sure to keep an eye on anything unusual,” Bhaghani said prior to the public gathering. “We are vigilant of anyone who will have any intention to hurt somebody else. We keep our eyes open.”

Authorities are probing whether Syed Rizwan Farook and Tashfeen Malik, the couple who killed 14 people and were later slain in a gun battle with police, were part of a broader network.

Enrique Marquez, a friend and neighbor of Farook’s who purchased weapons used in the shooting, is being questioned by the FBI. Officials say there is no rush to charge Marquez as long as he is cooperating. They believe charges are likely.

FBI Director James B. Comey testified this week that there is no evidence of a “sleeper cell” here or of any direct operational ties among Farook, Malik and foreign terrorist groups.

And yet a striking element of the case is that, in the hours before their deaths, the killers took pains to cover their tracks and keep anyone from examining the digital records of their communications.

FBI forensic experts are trying to tweeze data out of two smashed cellphones that have been flown to Quantico for examination, and here in San Bernardino, police divers are scouring the bottom of a lake about two miles from the site of the Dec. 2 massacre. Authorities have said they think the killers tossed a computer hard drive into the water at some point during the day of the attack. Television crews saw a diver hand something to someone on shore Friday, but the FBI has not said whether it is materially significant.

“I don’t think there is some golden nugget at the bottom of the lake that is going to tell us all,” said a senior U.S. law enforcement official. “It’s a dumping ground.”

The diving continued Saturday as residents stood nearby on the shore of the lake feeding bread crumbs to geese.

This is a vast suburb of Los Angeles, with the usual traffic jams and noisy freeways. It is framed by soaring mountains that were in rare majestic form Saturday after rain and wind blew away the smog.

Near the Inland Regional Center, where Farook and Malik went on their rampage, people gathered Saturday at a makeshift memorial to tie ribbons on a fence, write messages and leave flowers.

“I think people are angry,” said Virginia Nelson, who had picked up her sister at the airport and stopped to see the massacre site.

The Inland Empire, as this area is known, is a place for people on a budget, families with steady employment but not wealth. The low housing prices have drawn immigrants of many nationalities, plus their first-generation offspring. In Corona, an Episcopal church is a short stroll from the Islamic Society of Corona-Norco mosque, which is expanding and has 5,000 people at holiday prayer services - so many that they have to worship outside in a public park.

Many of the Muslims who came to the Corona mosque Friday said they had never experienced any prejudice or hatred. But many also said that the atmosphere has changed as a result of the terrorist attacks in Paris and San Bernardino and the inflammatory rhetoric from GOP presidential front-runner Donald Trump, among others.

“Dad, should I tell people I’m a Muslim?” a 9-year-old girl asked her father, Mohammed Halisi, a Jordanian-born local businessman, one day this week after school, Halisi said. He told her to respond that she is a Muslim, and that there are good and bad people in every religion.

“I love this country. I will die for this country if I have to defend it,” Halisi said.

Fauzia Rizbi, 41, spoke of her affection for American culture. She said she immigrated to California from Pakistan at age 14 and was soon introduced by a high school friend to the glories of American football, specifically the Green Bay Packers.

“I want people to know: I wear the headscarf, it doesn’t change anything,” she said.

Rizbi said she has been heartened by the community’s support for her. Shortly after the attack, a woman she’d never met gave her a hug at a grocery store.

Shabana Haxton, who chairs the interfaith committee at the Islamic Society of Corona-Norco, said her daughter, who wears a headscarf, has occasionally been the target of teasing at school.

“They say, ‘So are you going to blow us up? Do you have a gun in your bag?’ “ she said. “I tell her, ‘This is your chance to shine. Let them know by your mannerism - the way you react. If you’re going to get angry - no, that’s not what Islam teaches us.’”

Kuznia and Crandall are freelance writers. Sari Horwitz in San Bernardino, California, and Adam Goldman, Paul Kane and Julie Tate in Washington contributed to this report.