Despite a two-month investigation, the Maine Forest Service has been unable to identify exactly what malfunctioned on a southbound Pan Am freight train, creating a shower of sparks that triggered a 3-mile swath of fires along tracks in May.

Sparks from the train caused 47 separate fires along tracks from Scarborough to Biddeford, state investigators announced Thursday, the first time the freight train has been officially blamed for the fires, although witnesses suggested it was the most likely cause. Several reports by individual investigators suggest some sort of brake problem may have been the culprit, but the official conclusion was that the sparking was caused by “an undetermined mechanical problem” with the southbound train, which is owned by Pan Am Railways.

Forest Ranger Matthew Bennett, the lead investigator, said the case was unusual because “it was not associated with a poorly maintained spark arrestor or some other mechanical failure that provides clear physical evidence.”

The fires ignited hundreds of railroad ties, threatened dozens of homes and destroyed 10 seasonal trailers at the Wagon Wheel Campground in Old Orchard Beach. In all, it likely caused hundreds of thousands of dollars in damage, according to a 554-page report released Thursday by the Maine Department of Agriculture, Conservation and Forestry.

“There were multiple reports of sparks, the smell of burning rubber and smoke coming from the Pan Am southbound freight train immediately preceding the start of the wildfires,” the report said.

The fires were fought by 75 firefighters from 20 communities, some as far away as York and Windham. A Forest Service helicopter was brought in to drop water and people who live near the track used garden hoses to help contain the fires.

Bennett said the weather on May 8 contributed. It had not rained in days and there was some wind, he said.

“It was kind of a perfect storm for fires to occur,” Bennett said.

The investigation, led by forest rangers, found there was no violation of state law and there are no charges pending against the railroad concerning the fires. Rangers respond to and investigate an average of 40 railroad-caused fires annually in Maine.

Witnesses told investigators the freight train was noisier than most, making loud squealing, clacking and thumping sounds, and that sparks showered from beneath the train. Investigators determined an Amtrak passenger train that passed through the area shortly before the freight train did not contribute to the fires.

Forest rangers stopped the train in Dover, New Hampshire, to inspect it after the fires broke out. The train, designated DO1, is a local delivery train that carries goods from Rigby Yard in South Portland to Dover. It had about 50 cars and was loaded with frozen fish, steel, plywood and other wood products.

Bennett said investigators will likely never know for sure what caused the sparks.

“Normally when a train starts a fire, we can find something wrong with the train, like an arrestor crusted with carbon, a flat spot on a wheel or a brake shoe worn to nothing,” he said.”We didn’t find anything like that.”

However, in one of his reports, Bennett raised the possibility that a brake problem was the cause, and suggested the inspections made right after the fires – by members of the freight train crew as well as investigators – might have missed a brake problem.

“One other possibility is that a loose or errant brake shoe fell off a freight car onto the tracks and was pinched between the track and wheel,” he wrote.

Investigators did find brake parts at different locations on the track, including where the fires were most fierce.

“Brake shoe fragments were found on the tracks near the Wagon Wheel Campground, specifically along the northerly rail,” Bennett wrote. The fires were predominantly on the northern side of the tracks. “Also found in that area was slag from heated metal. I could not say whether that specific brake shoe fragment came from Pan Am DO1 or Amtrak 684,” he said, using the designations for the two trains that passed through the area within minutes of each other.

Cynthia Scarano, an executive vice president for Pan Am Railways, did not return a call for comment.

The investigative report includes internal company communications indicating that crews inspected the trains and found no mechanical problems that might have contributed to the fires.

Total damage estimates are still being tallied by victims and insurance companies, but are expected to be in the hundreds of thousands of dollars, according to the report. Bennett said property owners lost fences, lawn equipment, sheds and snowmobiles in the fire.

Railroads in Maine are responsible for compensating fire departments that respond to fires caused by trains. Pan Am Railways has a department to handle claims from property owners who seek damages.

Staff Writer David Hench contributed to this report.