Staffy suffocated by intruder in Melbourne backyard

An intruder has suffocated a Staffordshire bull terrier cross by wrapping duct tape around its head, leaving an elderly Melbourne widow heartbroken.

Police on Monday described the case as an "horrific" act of animal cruelty.

Nine-year-old Toby died in the backyard of his 71-year-old owner's Craigieburn home on Tuesday.

The widow adopted the dog from the Lort Smith Animal Hospital five years ago as a companion.

Detective Sergeant Peter Griffiths believes it was a random attack because there'd been no prior reports of Toby being a nuisance.

"This was a lovely-natured dog, it wouldn't harm anyone," Det Sgt Griffiths told reporters on Monday.

"It certainly assisted in the offender or offenders being able to tape the dog's mouth together."

Detective Senior Constable Lee Barton said it was a "despicable act" on a friendly rescue dog.

Anyone who saw someone acting suspiciously near the Abercarn Avenue Reserve in Craigieburn on Tuesday night is being urged to contact Victoria Police.