A Florida mosque where Pulse nightclub shooter Omar Mateen prayed was “intentionally” set ablaze in an early morning fire, authorities say.

According to the St. Lucie County Sheriff’s Department, a surveillance video captured a person approaching the Fort Pierce Islamic Center shortly before a fire broke out. Officials are investigating the incident as an act of arson.

According to the Sheriff Department’s Facebook page, the St. Lucie County Fire District, the Florida State Fire Marshall’s Office, the Bureau of Alcohol, Tobacco and Firearms and the Federal Bureau of Investigations are also assisting in the investigation.

Mateen, the ISIS-inspired guman who shot and killed 49 people during his June rampage, had attended the mosque regularly since 2003, CNN reports. The mosque was also attended by Moner Mohammad Abu-Salha, an American suicide bomber in Syria.

The Sheriff’s Department expects to release video from the fire soon with hopes that someone will be able to identify the individual who is believed to have started the fire.

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