Dozens of firefighters responded to a fire at a vacant triple-decker house in Waterbury on Thursday morning and representatives of the fire department said it appeared suspicious.
The second and third floor of 61 Giles Street suffered heavy damage, while the first floor sustained water damage.
The fire was reported just before noon and is believed to have started on the third floor.
No injuries are reported.
The fire marshal is investigating the cause.
Giles Street is blocked as firefighters respond.