A fire that destroyed a building at the shuttered Lake Grove School on Friday afternoon was intentionally set, Suffolk police said.
The fire was reported at 3:43 p.m. and was still smoldering at night, forcing firefighters and emergency services officials to take steps to raze the structure, police said.
No injuries were reported.
Police are asking for the public's help in finding whoever is responsible for the blaze.
A fire on Aug. 8 damaged a different building on the same property, according to police.
Lake Grove, which closed in June 2013 amid financial troubles, was a special education school and residential facility that served roughly 40 children.