The state police fire marshal is investigating a blaze this morning that destroyed a vacant house on Davis Lane in Slippery Rock Township.

A neighbor spotted the fire and notified the owners, Frank and Betty Davis, who live nearby on their farm that spans about 100 acres.

The neighbor, who called 911 about 8:15 a.m., also reported seeing an unknown man wearing a back pack and carrying an American flag walking near the house shortly before the fire.

Chief Steve Bickel of the Harrisville Volunteer Fire Company, said he passed that information onto the fire marshal. But he said it was premature to call the fire suspicious.

The two-story house had been vacant for "many years," Betty Davis said.

Her husband converted the house into a woodworking shop, which was equipped with utilities.

"I lost all my tools," Frank Davis said.

He estimated the value of those tools at more than $20,000.