Arsonist sets fire to mosque attended by Pulse nightclub shooter

Omar Mateen killed 49 people inside Orlando club

FORT PIERCE, Fla. - A fire at the Florida mosque where Pulse nightclub shooter Omar Mateen had prayed was deliberately set, the St. Lucie County Sheriff's Office said.

The fire broke out early Monday morning at the Islamic Center of Fort Pierce. Mateen, who killed 49 people at the Orlando nightclub in June, had attended the mosque.

No one was inside when the fire started, authorities said.

Video shows a person approaching the side of the mosque, followed by a flash. The person is then seen fleeing, Maj. David Thompson of the sheriff's office said.

Firefighters extinguished the blaze. Photos released by the sheriff's office showed the structure appeared to be intact.

Authorities were trying to make sure the building was safe before going inside to assess the extent of the damage, Thompson said.

It's not clear exactly how the arsonist set the building on fire.

Mateen had attended the Fort Pierce Islamic Center since 2003, Imam Syed Shafeeq Rahman told CNN earlier this year. Mateen had usually come for Friday prayers before the rampage at the Orlando nightclub on June 12 that killed 49 people.

Rahman said the mosque preached a peaceful message.

"So far as we here in Fort Pierce are concerned, we are always very conscious -- consciously speaking about peace, about love, about unity," Rahman told CNN in a previous interview. "We came to this country; this country gave us everything."

The mosque had also been attended by Moner Mohammad Abu-Salha, a Florida man who became the first known American suicide bomber in Syria.

One of the attendees at the mosque told CNN that the Fort Pierce Islamic Center was "like any other mosque."

"It's simple, friendly," Bedar Bakht told CNN in June. "Our imam is very good at explaining things. We never hear any stupid things coming out from anybody. It's very 

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