Butler police are investigating if a house was burglarized before it was deliberately set on fire Sunday morning, authorities said.

The fire at 510 Fairground Hill Road was reported about 5:40 a.m., just 30 minutes after the family there had left to go to a flea market.

No one was injured but the two-story house with an attic was badly damaged, leaving Thomas Sawicki, his wife and their 12-year-old son homeless.

“There appears to be some sort of criminal activity prior to the fire,” Butler police Capt. David Dalcamo said. He would not elaborate on the criminal investigation.

However, police and fire officials reported they found a collection of guns had been removed from the house, suggesting a possible break-in before the fire.

“The fire was intentionally set and started in the second-floor front bedroom,” said Trooper Duwayne Baird of the state police fire marshal’s office in Butler.

Baird said there were no immediate suspects in the arson.

Butler Fire Chief Nick noted that firefighters did not have to force their way into the house.

“The front door was not secured,” he reported.

That finding seemed to alarm Sawicki.

“I know all the doors were locked before we left,” he said.

Firefighters also found other evidence that suggested the home had been burglarized. The air conditioning unit in the rear bedroom had been removed and was on the roof of the back porch.

Next to the AC unit was a gun.

“Firearms, knives and other personal effects were also found in the rear of the house,” Ban said.

Sawicki said he knew nothing of how any of the items got there. He was convinced his house had been hit by burglars prior to the fire.

A plastic gas can near the back of the house raised more suspicions.

Dalcamo said police were investigating how the can got there. Sawicki said he always kept it in the garage behind the house.

Firefighters had the blaze under control within 30 minutes.

Firefighters left about 7:30 a.m. but had to return when the fire rekindled.

Ban estimated damage at $40,000 to the structure and an additional $25,00 to its contents.

Sawicki has insurance.

The VA Butler Healthcare’s rapid intervention team assisted the city fire department.

Sawicki said his family are temporarily staying with relatives.