Residents in Boyanup and College Grove were left outraged following a series of kangaroo shootings earlier this month.
According to landowners in the area, the culprits trespassed onto private properties and shot several kangaroos, between 12.30pm and 8.30pm on Saturday, April 6.
Police attended after being notified by staff at Bunbury Regional Prison. However, the officers were unable to locate the offenders.
One landowner discovered 20 kangaroo carcasses, all with their heads blown off and hind legs removed.
Residents believe the culprits used high powered rifles and shotguns to kill the kangaroos.
Centenary Road resident Tamara Warren said her family and their neighbours' horses were startled by the gunshots.
Mrs Warren said they were all sickened by the culprits' actions.
"I can say with certainty that this was not done by a farmer, because of the way they left the carcasses," Mrs Warren said.
"If you're going to shoot, you must get a damage permit. Police have to be notified so that they can notify the prison.
It was devastating...it was unnerving, for a couple of days. I am very thankful that none of us were hurt."
Those with information have been urged to contact Crime Stoppers on 1800 333 000 or Bunbury Police on 9722 2111.
"RSPCA Western Australia understands WA Police are investigating a number of kangaroos found dead and mutilated on a property near Bunbury," RSPCA WA chief inspector Amanda Swift said.
"While we cannot make public comments about an active investigation being undertaken by another regulatory body, we are deeply concerned to hear about any instances of cruelty against vulnerable animals."