Police are yet to speak with a man who survived a fire in Melbourne's south east that killed a 38-year-old woman and her three children.
Victoria Police acting deputy commissioner Robert Hill on Monday said the 50-year-old man, believed to be related to the family, remained at the Alfred Hospital in a serious condition.
"We will speak to the survivor," he told reporters on Monday.
"He may or may be able to shed some light in terms of how the fire commenced."
The man has not yet faced any charges, with authorities unlikely to confirm the cause of the fire until later this week.
"We have not made any determination whatsoever in terms of the cause of that fire and speculation is not part of our business," acting dep comm Hill said.
"We will understand the facts and the circumstances before this matter is progressed."
The Japanese Embassy has been contacted in relation to deaths of the woman and her children, aged three, five and eight, he added.
They would also be questioned in relation to whether there was a history of conflict between the man and woman.
The fire started in the garage and the family was found in an upstairs ensuite.
Emergency services were called to the house in Glen Waverley about 1.40am on Sunday.
Fire Rescue Victoria crews arrived to find the garage of the property well alight, and thick smoke filling the two-storey house.
Thirty-five firefighters were needed at one point to bring the blaze under control.