Officials said Thursday that the 10-alarm fire that tore through an apartment complex under construction in Waltham, Massachusetts, last month was intentionally set.
A $100,000 reward is being offered by the property owner and contractor for information leading to the arrest of the person responsible.
Four firefighters suffered minor injuries fighting the blaze that tore through the complex on Cooper Street on July 23. Nineteen area fire departments helped battle the flames.
"This was very dangerous. It was a long battle," Waltham Fire Chief Paul Ciccone said. "When someone commits a criminal act, I think it angers everybody because these are risks we shouldn't have to endure."
Anyone with information about the fire is being asked to contact the state's arson hotline at 1-800-682-9229.
"We now move from the origin and cause investigation into the criminal aspects of this investigation," State Fire Marshal Peter Ostroskey said. "We need the public's help to solve this case."
The general contractor, Callahan Construction, was slated to finish 264 luxury apartments by the end of the year. The damage was estimated at $110 million, according to Ciccone.
In addition to the damage at the construction site, authorities said at least 30 vehicles at nearby E & T Auto Body on Elm Street were destroyed.
Nearby homes, including about 150 people at the Arthur Clark Apartments, an elderly housing complex, were evacuated due to the amount of smoke.