The device turned out to be a fake, authorities said.
"It contained no explosives," said Carrie Adamowski, a spokeswoman for the FBI's Philadelphia office, which spearheaded the investigation.
The device was filled with screws and the flares could not be ignited, the Prosecutor's Office said.
Still, Adamowski said, "it appeared that someone put some time into it and was hoping to make it look legit."
The building was cleared, and the Camden County bomb squad detonated the device about 11 a.m. The federal Bureau of Alcohol, Tobacco, Firearms, and Explosives also responded.
"You would never think this would happen in a small town, but it opened our eyes to the world we're living in," said Police Lt. Lloyd Lewis.
Wardlow, who has been mayor since 2010, is retired from the financial industry, Borough Solicitor Morris G. Smith said.
She was not in the building Thursday morning.
"Our borough has no reason to think that anyone is specifically targeting our mayor," Smith said.
Wardlow did not return a call Thursday seeking comment.
Smith said she was "in good spirits" and concerned for employees' safety.
Borough offices closed early, Smith said, adding it was the mayor who felt employees should be given the rest of the day off.
Authorities asked anyone with information to contact Fred Lang, an investigator with the Prosecutor's Office, at 609-381-4940.
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