A mosque where Orlando gunman Omar Mateen once worshipped was set on fire early Monday by an arsonist who apparently fled after being caught on security video, authorities said.
No one was inside the Islamic Center of Fort Pierce when the attack took place just after midnight, police said.
Firefighters were called to the mosque at 12:31 a.m. by reports of flames coming from the building's roof, authorities said. It took them nearly five hours to extinguish the fire.
Investigators obtained footage from the building's surveillance cameras, which captured a man in embroidered jeans and a wide-brimmed military-style hat arriving on a motorcycle at 11:38 p.m., carrying what appeared to be paper and a bottle of liquid, the St. Lucie County Sheriff's Office said.
The footage shows the man approach the building, then a flash, then the man running away. After the flash, he briefly waves an arm, which investigators believe may have been a response to getting burned.
The extent of damage to the mosque was unclear. Fire department dispatch recordings include reports of a quarter of the building on fire when firefighters arrived.
Local and state officials are investigating the crime, and have asked for help from the U.S. Bureau of Alcohol, Tobacco Firearms and Explosives and the FBI.
Major David Thompson of the St. Lucie County Sheriff's Office declined to speculate on why the attacker struck the mosque, but the fact that it happened the morning after the 15th anniversary of 9/11 "is in the back of our minds."
The mosque is known as being one of the places Mateen attended prayers in the months before he killed 49 people at the Pulse nightclub in Orlando in June.
Monday's attack also coincided with the start of one of Islam's holiest times of the year, Eid Al Adha. The sheriff's office already had deputies assigned to provide security for services at the mosque. But now members of the congregation will worship elsewhere, the mosque said in a statement.
"Please keep us in your Du'as and prayers," the mosque said in a statement, using a term for "invocation."