FORT PIERCE, Fla. (AP) — The mosque that Orlando nightclub gunman Omar Mateen attended was set on fire in what Muslim leaders said Monday was the latest incident in an escalating campaign of harassment and violence against the house of worship and its members.

Given the timing – Sunday’s 15th anniversary of 9/11 and the start of the Muslim holiday Eid al-Adha – investigators believe the blaze that broke out shortly before midnight Sunday at the Islamic Center of Fort Pierce may have been a hate crime, sheriff ’s spokesman Maj. David Thompson said.

No one was injured. The fire burned a 10-by-10-foot hole in the roof at the back of the mosque’s main building and blackened its eaves with soot.

A surveillance video from the mosque showed a man approaching the building with a bottle of liquid and some papers, then leaving when there was a flash and shaking his hand as though he may have burned it, Thompson said.

Mateen was killed by police after opening fire at the Pulse nightclub June 12 in a rampage that left 49 victims dead and 53 wounded. He professed allegiance to the Islamic State group. His father is among roughly 100 people who attend the mosque.

Wilfredo Amr Ruiz, a spokesman for the Council on American-Islamic Relations, said the mosque and its worshippers have been harassed since the massacre.