Once inside the two-bedroom suburban brick-and-tile house, police discovered the bodies of Mara Harvey, her three daughters - two-year-old twins and a three-and-a-half year old - and the girls' grandmother Beverley Quinn.
Officers discovered the bodies of two women and three young children in a house in Bedford on Sunday afternoon at 12pm local time.
"The man now assisting police remains in custody", police said on Monday.
"That will take a period of time and it could be a number of days", Assistant Police Commissioner Paul Steel said.
A MAN has surrendered himself at a regional WA police station this morning, revealing a killing spree at a home in the Perth suburb of Bedford. No further information was provided on the victims and the man in custody.
Coode Street resident Richard Fairbrother, who lives next door to the house where the bodies were found, said he last saw the family more than a week previously, as he had been away.
Police said there are no ongoing safety concerns for the community.
Neighbors said a young family lived in the home and an older woman had frequently visited. He was questioned, but it's unclear if he's related to the victims and no charges have been laid yet.
Investigators are now searching the home for evidence, and police could not provide any further details on the victims.
He said forensic teams were on the scene and investigators were trying to piece together a timeline of events.
"It's just so sad, they've got primary school aged kids and I thought it just couldn't be", she said.
"This is a tragic event and will have an impact on family and friends, the community, and the emergency services who first responded to the tragic scene".
"It's sickening to think someone could do that".
It has taken everyone by surprise, we are all in complete shock.
"They were a flawless family. this is a handsome neighbourhood, it's quiet", Alfie said.
"It's just horrific on every level".
Police forensics at the home of the family found dead in Perth.
A grandfather shot dead his wife, daughter and her four children in murder-suicide in May.