The man, aged in his late 40s, and a woman in her early 50s were found dead in their rented granny flat on Wednesday night in northern Sydney.
Officers conducted a welfare check on the Forestville couple after neighbours expressed concern that they hadn't seen the two in the northern Sydney suburb since Saturday.
The couple were both found with lacerations to their bodies.
Their cause of death remains unknown but detectives have not ruled out the case being a domestic-violence-related murder-suicide.
Neighbour Coco Hau said she had spoken with the man multiple times, as he had caught her kids climbing a tree that overlooks the granny flat and her home.
"The husband has got a hot temper," she told AAP.
"My kids sometimes climb up the tree and play with their dog and get told off a couple of times.
"I've realised it (the dog) hasn't been barking for some time.
"His partner is very quiet, only the man ... could be noisy."
The granny flat sits behind a three-storey mansion on what neighbours described as a "quiet suburban street".
The couple's two dogs and a cat also found in the flat have been taken to a local vet.
Paul, another neighbour said he was picking the bins up at 8am on Thursday when he looked over to see the police tape and officers surrounding the property.
As a long-time resident, he said he can pick the faces of the owners but not the tenants.
"I don't know the people there, but I know the faces (of the owners)," he told AAP.
"(The owners) moved in a few years ago, they walk past the house and we say g'day."
While the bodies are yet to be formally identified, the couple is known to have lived in NSW for a few years after moving from Queensland.
"We are treating the investigation as suspicious at this particular point in time," Detective Superintendent John Duncan said.
"All I can say is there are two bodies in there. They have got lacerations to them."
A white van in front of the property was also seized by police, although Supt Duncan did not comment on the van's significance to the case.
He appealed to the public to notify police of any suspicious activity in the area in the past four days while noting it did not appear a third party was involved.
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