Authorities are investigating a possible arson after two parked cars were found ablaze outside an environmental activist’s home in Mililani.

When firefighters arrived at Carroll Cox’s home at about 11 p.m. Wednesday, the fire was already extinguished, Honolulu Fire Department spokesman David Jenkins said.

Cox told firefighters he was inside the house when he heard an explosion and went outside to find his two cars on fire. Jenkins said Cox doused the flames with a garden hose and an extinguisher.

One car was parked in the driveway and the other was partially in the carport, Jenkins said.

Cox told Hawaii News Now he believes he was targeted as retaliation for his investigations into illegal dumping and leases on land owned by the Department of Hawaiian Homelands.

"No, it will not deter my work, because I’m not doing anything wrong," he told the news station. "I’m doing what I do to expose waste, fraud and abuse."

Jenkins said it appears flares were used, an indication of possible arson.

"Police will do the final determination if it’s arson," he said.

A police spokeswoman said an arson investigation is underway.

Damage to both cars is estimated at about $3,000, Jenkins said.