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DERRY TOWNSHIP (KDKA) — A forest fire specialist believes a serial arsonist is on the loose in Westmoreland County.

Police and military helicopters were called around 5 p.m. Thursday to a remote site in Derry Township along Pizza Barn and Akney roads. Investigators say a fire set there has been ruled arson.

They have also identified a person of interest.

The reason the forest fire specialist in the case believes Thursday’s fire is the work of a serial arsonist is because he says it’s at least the fourth fire set in the last three years.

They also all have similar characteristics, according to the investigator.

Fire departments from Derry, Blairsville and Bradenville all responded, along with the Westmoreland County Rough Terrain Fire and Rescue Team.

Volunteers were on the ground, and state police and National Guard helicopters were in the air to assist.

Brian Vinski, a forest fire specialist with the Department of Conservation and Natural Resources Bureau of Forestry, tells KDKA News this is at least the fourth fire since 2016.

Vinski says all four fires have a similar char pattern, which makes him believe they are all linked.

“[Residents] just need to be vigilant if they see anything suspicious, you know, to report it. If there are fires in their neighborhood and there is no clear cause, notify my office so we can follow up,” he said.

The fire investigator says there is a person of interest, but no name or description is being given at this time. Investigators do believe the suspect is driving an ATV to the scenes of the fires.

Additionally, because these types of fires are set in very remote areas out of sight, the pieces take time to investigate, Vinski says.

Anyone who sees anything suspicious is urged to call the fire investigator’s office at (724) 238-1200.