A Maine man fatally shot his parents and a couple in their Portland-area home before firing at passing cars on an interstate where he hit three members of another family, critically injuring one, police said Wednesday.

Authorities arrested Joseph Eaton, 34, on Tuesday within hours of discovering the bodies in the small town of Bowdoin and said he has confessed. Eaton has been charged with four counts of murder but could face more charges, authorities said, citing the ongoing investigation.

“This stuff doesn’t happen in Maine,” Maine State Police Col. Bill Ross said. “Right now we’re in the ‘how’ phase, how this happened. And I think the ‘why’ part of this, why did all of this happen, will come at a later date.”

Investigators say they believe Eaton’s attack was an isolated incident and there is no ongoing threat to the public.

Who was arrested for Maine shooting?

Eaton had been released from a Maine prison on April 14 after serving an approximately two-year sentence for assault. Under Maine law, he was barred from possessing firearms because of his prior convictions.

Police said Eaton shot his parents and their friends at a home and barn in Bowdoin, then fled onto nearby I-295 where he began firing at passing cars, believing he was being chased by police. He then ditched his vehicle and was caught nearby, police said.

Eaton is being held at Two Bridges Regional Jail. His mugshot is not being released at this time, police said. They also declined to discuss the kind of firearm they recovered from near his vehicle.