A crowded prayer vigil was held at the Islamic Center of Riverside -- the same mosque the shooting suspect Syed Farook attended regularly for years. No one expected what he was capable of.
"No red flag ... never heard from any community member," said Mohammad Ashrif, the Islamic Center of Riverside Board Chair.
The San Bernardino massacre -- the actions of Farook and his wife, Tashfeen Malik -- is now being investigated by the FBI as an act of terrorism.
It adds to the stress of many in Anaheim's Little Arabia, who say they fear a backlash.
"The community is in shock and fear. It's real fear of terrorism, it's real fear ... people are afraid," said Bill Dalati, an Anaheim businessman and an American Syrian.
Dalati says he's received calls from Muslim women concerned about wearing their veils.
"They're asking is it OK to take it off or should we take it off?" he recalled. "We're very afraid for our safety for our kids safety."
At the prayer vigil in Riverside, the message was clear. As they condemned the horrific attack, they extended their sympathy to the victims and their families.
Leaders urged Muslims not to change how they dress or how they appear, and not to be afraid to come to worship.
"This is the time to do your life as normally as you've done it before," Hussam Ayloush, the executive director of CAIR-LA, told the crowd. "We are not less American than anyone else and we will not allow any other person to make us less human or less American."
Ayloush added, "Don't let anyone divide the community -- not terrorists, or murderers."
Leaders also urged Muslims to stay vigilant: If they see anything or anyone suspicious, report it to law enforcement.
At the same time, Muslim leaders said they hoped the investigation will provide more information to help better explain how someone who worshiped alongside them could turn into such a monster.
Local Muslims fear backlash from San Bernardino attack
SAN BERNARDINO MASS SHOOTING