A flock of sheep was attacked by a dog, killing one and leaving 25 injured.
It happened on farm fields near Wotton-under-Edge in Gloucestershire on Thursday night between 22:00 GMT and midnight.
It is thought five of the injured sheep will have to be put down because of their injuries.
Gloucestershire Constabulary did not detail the precise circumstances or the breed of dog involved but the force wants witnesses to come forward.
Officers want to hear from anyone who saw anything suspicious near the Bournstream layby on the B4060, or on Old London Road close to the public footpaths that enter the adjacent woodland.
They are also keen to identify the owner of a camper van reported to have been parked on Old London Road on Thursday night.
Allowing a dog to worry or attack livestock is a criminal offence.