WALTHAM (CBS/AP) – A fire that broke out at the site of a controversial holiday lights display in Waltham early Thursday morning was intentionally set, investigators said. A $5,000 reward is being offered for information that leads to an arrest.

Firefighters found heavy flames coming from the back of the vacant administrative building of the former Fernald Center off Trapelo Road when they arrived just after midnight. They were able to put the fire out pretty quickly.

Just last week, the Waltham Lions Club opened its drive-thru fundraiser light show on the property, which has been vacant for years.

Some have been protesting the display because of the property’s history. The Fernald Center, which moved to Waltham in the late 19th century, became a place where the developmentally disabled, including those with cerebral palsy and Down syndrome, were shut away from a society of which they were deemed unfit to be a part.

Waltham Deputy Fire Chief Roger Hebert said the fire was not caused by the light show.

“I have asked that already and not at all, nothing to do with that building at all, their power came from a second unit, so it had nothing to do with that building,” he told reporters.

“This was an intentionally set fire causing extensive damage to the basement level of the Fernald Administration Building,” State Fire Marshal Peter Ostroskey said in a statement.

One firefighter had a minor injury and was treated at the scene. The exact cause of the fire is under investigation.

Anyone with information about how it started is asked to call the Arson Hotline at 1-800-682-9229.

(© Copyright 2020 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)