Fire broke out inside an abandoned mill in East Hampton on Sunday.
Firefighters responded to the building at 13 Summit Street around 11:45 a.m. and found heavy smoke coming from the windows on the second and third floors.
The building, which operated as a turn-of-the-century mill, is a known hazard and is often used by vagrants, according to East Hampton fire chief Greg Voelker.
The fire was located in a room on the second floor.
There is no electricity to the building and there was no natural source of ignition, so the fire was most likely intentionally set, Voelker said.
No one was inside when firefighters arrived.
Fire crews from Colchester, Haddam Neck, East Haddam, Marlborough and Portland were called to assist and the fire was put out in about 30 minutes.
The local and state fire marshals will handle the investigation.