On a dead end street in Brockton, someone apparently targeted the mayor's car.
Neighbors thought it was an explosion.
"Sounded like a very loud bang," said David Simoes, who lives across the street. "Not your average firecracker ...something very big."
Robert Moore owns the home that the mayor rents.
"There was an explosion of some type," said Moore. "And my son-in-law went out. And under the car...it was some kind of container."
Investigators believe it was arson and they're offering a $5,000 reward for information.
The 2015 Ford Explorer is owned by the city and used by Mayor Bill Carpenter.
Since then, police have been guarding the neighborhood.
"Glad to see they're not just letting this slide by," said Simoes. "They're all over this."
It happened late Friday night or early Saturday morning.
The mayor wasn't home at the time, and nobody was hurt.
Investigators have not said what the possible motive for the crime may have been.
"He's done a good job with the city," said Moore. "He's obviously made some enemies, more friends than enemies, but there's always some nitwit that probably pulled some kind of a foolish thing like that."
In a statement, the mayor says in part "...We appreciate all the concern...this is a difficult time for my family and I. We have faith in the state and local public safety agencies involved to complete a thorough investigation."
Carpenter was in Cape Verde at the time and just returned Wednesday. He lives at the home with his family.