COLLEGE PARK, Md. (AP) – Investigators believe a massive fire that destroyed a 6-story building under construction in College Park was accidental.

Prince George’s County fire officials said in a statement Thursday that a preliminary investigation shows the fire was not intentionally set.

The exact cause and origin of the fire remain unknown. Officials say that investigation could take weeks.

The fire on Monday burned throughout much of the day and was one of the largest fire suppression efforts in the county’s history. Heavy smoke and poor air quality prompted the nearby University of Maryland to cancel classes. The building was to include both apartments and retail. The cost of the damage was estimated at $39 million.

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