The Tuesday night fire that damaged a two-story garage apartment in Butler is considered suspicious, authorities said.

The building that houses the apartment at 307 N. Bluff St. had been vacant since June 25 when it was condemned following a fire at the adjoining garage apartment.

“It’s suspicious because there were no utilities connected and because no one was supposed to be living there,” Butler Fire Chief Nick Ban said today.

State police deputy fire marshal Trooper David Jungling is investigating the cause of the blaze that occurred after 9 p.m.

Fire crews arrived and found heavy smoke coming from the building. Firefighters found the fire had started in the rear of the ground floor apartment, which recently had been used as a one-room efficiency.

The flames spread to the second floor.

Firefighters got inside through a second-floor door and put out the fire.

Damage in Tuesday night’s fire is estimated at $15,000. The property, owned by David Schultz of Renfrew, is insured, authorities said.

The apartment is attached to another two-story garage apartment at 305 N. Bluff St. that was damaged in the fire two weeks ago.

The earlier fire, which caused only $500 in damage, started in the basement and was ruled accidental due to substandard wiring.

An inspection turned up numerous other building code violations, and city code enforcement officer Sean Gramz and Ban condemned the building.

The decision forced 13 tenants living at the building to find new homes.