A major police investigation has continued through the night after the deaths of a woman and her three children at a home in Melbourne's north-west.
The bodies of Katie Perinovic, her three-year-old son Matthew and two daughters Claire and Anna, aged seven and five, were found in their Tullamarine home on Thursday.
Tomislav Perinovic, 48, husband of Ms Perinovic and the children's father, called emergency services to report the deaths.
Police said he was assisting police with their enquiries on Thursday, but stressed with an ongoing investigation it was important not to speculate about what happened.
No-one has been charged over the deaths and homicide detectives do not believe anyone else is involved.
Asked if murder-suicide was a possibility, Acting Deputy Commissioner Bob Hill said: "There is a number of possibilities, and that's one that could possibly be relevant to this particular event".
Police declined to comment further on the investigation this morning.
A small number of detectives and uniformed police remained at the Burgess Street home during the morning and the house was cordoned off behind police tape.
'Smiley face Katie' was loved by the neighbourhood, friend says
Ms Perinovic, a physiotherapist, was described by neighbours as "the best mum" and "one of the nicest people you'd meet".
Another neighbour remembered the children as "gorgeous, very friendly and happy".
Neighbour and friend Marie Groves said a day later "it still hasn't really sunk in properly".
"It hasn't sunk in that I'm not going to walk out the door and see her walking past to the milk bar and picking up pizzas with the kids," she said.
"I'm not going to be able to be at the park and see Matthew jumping on the trampolines."
Ms Groves said her children were friends with Matthew, Claire and Anna, and Ms Perinovic was "such a feature of the neighbourhood".
"She was Katie, smiley face Katie, who would always stop and chat," she said.
She said the Tullamarine neighbourhood was still struggling to come to terms with the news.
"It's incomprehensible, we just cannot understand how this could have happened to Katie."
She said Ms Perinovic was proud of her physiotherapy work, which she returned to part-time when Matthew was old enough.
It was during the days when Ms Perinovic was home with the three children that she and Ms Groves bonded, she said, taking their kids to the park and watching them play together.
Acting Assistant Commissioner Mark Galliott said on Thursday the sudden loss of life, including three children, was difficult to comprehend.
"This will have long-lasting effects on the police that attended, on extended family, the community, the neighbourhood, the emergency services and everybody else involved," he said.
"They'll be lifelong memories that they'll have to deal with and so we'll make sure that the welfare of our members and the emergency services that attended are paramount."
Police urged anyone with information that may help with their investigation to contact Crime Stoppers.