A 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 Wednesday.

State police deputy fire marshal Trooper David Jungling is investigating the cause of the blaze that occurred shortly 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 and burned through the hallway floor, Ban said.

Firefighters got inside through a second-floor doorway and quickly put out the fire. The upstairs recently had been used as a two-bedroom apartment.

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 throughout the building.

But an inspection turned up numerous other building code violations including faulty gas lines.

City code enforcement officer Sean Gramz and Ban condemned the building. Peoples TWP and West Penn Power were notified, and gas and electrical services were disconnected.

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

Gramz sent Schultz a letter telling him that repairs would need to be made before occupancy could be restored.

Those code violations have not been corrected, authorities said.

Neighbors told investigators that they did not see or hear anything before Tuesday night’s fire, Ban said.

Jungling did not immediately return a telephone call Wednesday.