Police learned of the explosion on Wednesday, June 19, at 185 Madison St. They found fireworks, a butane gas can, and projectile materials at the scene, the Worcester County District Attorney's Office said.
Officers found two other unexploded devices left inside coolers last month.
Police are investigating who built those bombs.
Authorities ask residents to avoid unattended items and to call 911 immediately if they see anything suspicious.
“Massachusetts residents have caused themselves grievous injuries while attempting to create homemade explosive devices,” said State Fire Marshal Jon M. Davine. “These devices are illegal and potentially fatal.”
The warning comes after police exploded a bomb and other "energetic material" at a Haverhill home last week. Police arrested the man they say is responsible for that device.
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