LUSK, Wyo. (AP) — Niobrara County officials say they're investigating three explosive devices that detonated at three homes in Lusk.

Sheriff Rick Zerbe says two of the improvised explosives that went off March 6 were in the yards of a Wyoming Highway Patrol trooper and a school principal.

The Associated Press says a fourth bomb that didn't go off was found near the trooper's home. The Wyoming Office of Homeland Security sent a bomb technician from Casper to disarm the device.

Authorities are investigating whether the incidents targeted certain people or were random acts of mischief. They have not disclosed details about the explosives.

Lusk police urge people not to approach or handle any plastic bottle they find that has fluid in it, especially if the bottle is expanded or out of shape.