A 60-year-old New Jersey man was sentenced to six years in prison for severely injuring a 34-year-old man with a defective homemade explosive device at a Somerset County block party last summer, prosecutors announced Wednesday.

A judge on Friday sentenced Thomas Kaiser of South Plainfield, and his son, Erich Kaiser, 29, of Monmouth Junction, who plead guilty to charges after their “signal cannon” injured the man at Cooper Street Park in Manville last July, the Somerset County Prosecutor’s Office said.

Erich Kaiser was sentenced to three years probation, the prosecutor’s office said.

They were ordered to pay $76,000 in restitution for the bystander’s injuries. Both plead guilty in March to fourth-degree aggravated assault by recklessly causing bodily injury with a deadly weapon and criminal mischief. Thomas Kaiser separately plead guilty to second-degree causing or risking widespread injury or damage.

Attorneys representing the Kaisers could not be reached for comment by NJ Advance Media.

A community-wide party at the park was winding down when the men ignited the device. Investigators said the homemade cannon malfunctioned, rupturing and sending shrapnel across the area. One of its pieces struck the bystander, and shrapnel damaged property, including cars.

Investigators determined the makeshift explosive was improperly packed with Pydrodex power, an incendiary material. It ruptured because of the blast’s pressure, causing flying debris, the prosecutor’s office said.

Thomas Kaiser was previously sentenced in 2019 to one year of probation after dropping off homemade explosives to a member of a band performing on Labor Day weekend in Sea Bright.

A parade was canceled after police found explosive materials Kaiser allegedly left in a dumpster along the route.

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Eric Conklin may be reached at econklin@njadvancemedia.com.