More details have emerged after a woman and her three young children were found dead inside their Melbourne family home on Thursday.
Emergency crews found the bodies of 43-year-old Katie Perinovic and Claire, 7, Anna, 5, and Matthew, 3.
The 48-year-old father of the children, Tomislav Perinovic, made a frantic and distressing emergency call and was found by paramedics sitting in the front yard of the house.
Perinovic is being treated as a "person of interest" and has given his account of what happened to police.
Victoria Police told Daily Mail Australia Perinovic was still in custody and assisting investigators with their inquiries at 12.30am on Friday, 12 hours after he first called police in an "extremely distressed" state.
Acting Deputy Commissioner Robert Hill said while the investigation is in its very early stages, the woman and her children "died in suspicious circumstances".
"As to who is culpable for the death of the four people that is yet to be determined and we should not draw any conclusions at this point in time."
He said it would be "grossly unfair" to assume culpability on the basis that the father is assisting police.
"We just need to understand the facts, and unfortunately they're not known to us but will be in the fullness of time.
"We have a long way to go before we can actually understand and appreciate what occurred."
Asked if it could be a murder-suicide, police said there were "a number of possibilities and that's one".
Hill said police would work through the crime scene methodically and the man had provided police with his account of what happened.
"It is a tragic event to lose life, in any circumstances," he said.
"But when it involves three children — the second event this week where we've seen the loss of children in horrific circumstances — it does impact upon the community."
Acting Assistant Commissioner Mark Galliott said police would remain at the scene all night.
"The loss of young lives in circumstances such as this is are difficult to comprehend.
"This will have long-lasting effects on the police that have attended, on extended family, the community, the neighbourhood, the emergency services, and everybody else involved.
"They'll be lifelong memories that they'll have to deal with."
Galliott said information indicated the man was not injured.
There was no family violence history associated with this family, Hill said.
Police would not reveal details about any injuries the victims suffered.
A neighbour told NCA Newswire it was "awful".
"There's people everywhere, police everywhere."
She said she heard sirens about 12.30am but did not hear anything unusual beforehand.
"My son actually came and said 'you've got to have a look at this, Mum', when the commotion started."
Another woman who lives in the same street also said she did not hear anything before the police arrived.
"We were wondering what the hell is going on?".
"We've never seen this many cops in this area.
"It's so sad."