Mastiff puppy Chief and his elder companion Molly, a Staffordshire terrier, frequently enjoy morning strolls with their owner, Marcus Norton, in an off-leash zone located in Pinjarra, just south of Perth near Mandurah.

But when the pets approached a stranger and his dog three days ago, they were stabbed, and Molly was put down.

Veterinary surgeon Ashleigh Holgate from Waroona Veterinary Clinic noted that Molly had some age-related complications. It was determined that avoiding the stress of surgery would be “more beneficial for her”.

Chief’s back wounds are hoped to heal in the coming weeks.

Police say the attacker’s dog was also injured, suffering bite marks. 

They said the dogs were attacked with a “multi-use tool”.

It’s illegal to carry an edged weapon in WA without a lawful reason – like work or recreation. 

Self-defence is not a legal excuse. 

“This has cost us more than five and a half thousand dollars, that we don’t have, like, what the hell,” Norton said.

“He needs to answer for this.”

The other dog owner denied 9News’ request for a comment.

The investigation is ongoing.