Grewal's Arson Investigations Squad was working the case, the prosecutor told Daily Voice.
He couldn't confirm a report that someone who'd been ejected from an event at the hall earlier Tuesday night might have been responsible.
No injuries were reported in the 11:15 p..m. blaze, which occurred while the Maple Avenue building was vacant, Fair Lawn Mayor John Cosgrove said, adding that firefighters knocked it down within 10 minutes.
"Someone who was at the bar up the street says he saw someone throw something through the window," the mayor told Daily Voice.
The interior of the stone building sustained smoke and water damage, he said.
The arson report prompted Fair Lawn police to notify the prosecutor's investigators, who worked the scene overnight.
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