That is what confronted police when they busted into a Hillsdale apartment on Monday afternoon following the deaths of mother and son, Stacey Docherty and four-year-old Seth.

Twenty-four hours after the grim discovery, police say they are still keeping an open mind as to whether a third person was involved or if it was a case of murder-suicide.

Fairfax Media understands that rambling messages were written over the walls, some of which appeared to be in blood, when emergency services found the pair at 1.20pm on Monday.

Ms Docherty's ex-partner and the father of her son is believed to have raised the alarm when he knocked on the door and no one answered.

He took to Facebook on Tuesday to express his grief.

"I'm going through some gnarly process but will get through this," he said.

"I will post some pics of me and my son for those (many) who never had the pleasure of seeing him. I feel grateful for a brief time I got to be a father to a beautiful little boy.

"Vale Seth Bon Docherty."

It is unclear how the mother and son had died with police ruling out gas as the cause.

The mother-of-one listed her job on Facebook as a nursing manager from Christchurch, New Zealand, and filled her social media feed with photos of her son.

She posted numerous pictures of the pair at beaches and playgrounds as well as a photo of her fresh tattoo, a quote that says: "bad things happen when good people stand back".

In one post, she described her then two-year old son as a "gentle, smart boy".

On Tuesday morning, a police spokeswoman said it was still unclear what happened to the pair.

She said police were still investigating whether it was a murder-suicide or if another person was involved in the deaths.

"It's still very much under investigation," she said.

Ms Docherty was known to police after officers attended the street last year when she smashed three of her neighbours' cars with a bat following a dispute over parking.

"My dad's van was parked here, and she smashed the front and back window," one neighbour, Odysseus, said.

"I was at the local park and then [a neighbour] came and told me that she was going crazy here, and I came back and we all tried to stop her.

"She started swinging at my dad and saying racist stuff about Assyrian people, that we're all terrorists and that. Then police came and stopped her."

Though there were initial reports of a strong smell of gas in the apartment complex, police have since ruled that out as contributing to the mother and son's death.