An unknown arsonist likely started a fire that sent emergency crews scrambling to the International Woolen Mill in Sanford Monday morning, according to investigators from the Maine Fire Marshal’s Office.

Investigators determined the fire was likely set intentionally, officials announced Thursday in a news release.

Shortly before 9 a.m. Monday, smoke was reported billowing from the vacant mill. Local fire agencies arrived and were able to control the fire with no reported injuries, according to the press release.

Assistant Chief Brian Watkins, of the Sanford Fire Department, said the fires appear to be the result of arson due to there being several of varying sizes. The mill is a common site for encampments set up by unhoused people.

“A lot of the public feels that this was a warming fire,” said Watkins, “but it wasn’t.”

The mill, known as the International Woolen Mill, was built in 1923 and has been vacant for years.

Watkins said the building is a big concern for Sanford, so much so that they already have plans in place if a more substantial, dangerous fire were to break out in the building.

“It’s a very dangerous building. It’s a severe hazard to the neighborhood that surrounds it,” Watkins said, “… we have plans in place for protecting the residents of the bordering neighborhood in the worst-case scenario, and most of them include evacuation.”

The reason the city is yet to take the building down, despite its potential dangers, is the overwhelming cost. The company that purchased the mill most recently, Regco, Inc., no longer exists.

The Maine State Fire Marshal’s Office urges anyone with information about the fire to contact the Maine Arson Tip Line at 1-888-870-6162 or the Sanford Police Department at 207-324-3644.