Animal control officers have found eight dead cats -- all strays -- in one neighborhood, the Boston Herald reported Wednesday.
Whoever is killing the animals is "someone with quite a bit of aggression," Lawrence Police Chief John Romero said.
None of the cats had apparent injuries, Romero said. Police at first believed the cats had been poisoned, but the eighth cat, found last week, had been hit on the head, an autopsy revealed.
Romero said the injuries were not consistent with being hit with a car.
Animal cruelty is a felony in Massachusetts.