A suspected double murder of two young children in Yanchep on Thursday night is believed to have been carried out by their 35-year-old father Jason Headland.
Mr Headland, who remains in a critical condition at Royal Perth Hospital, is under police guard after he apparently tried to commit suicide following the death of his two children aged three and five.
Major Crime detectives forced entry to the children's Flight Vista home about 10.30pm on Thursday night to find the bodies of three-year-old Lily and five-year-old Andreas - who are thought to have been stabbed to death.
They also found their critically-injured father in the home and police later confirmed they were not looking for a third party.
According to neighbours Mr Headland had only recently moved into the Yanchep estate and it is not known if the mother of the children, Anatoria Headland, was living with them at the address.
She is thought to have been in Perth when she was delivered the tragic news.
WAtoday spoke to a neighbour, a father in his 50s, who said the family had just moved into the estate.
"We didn't know who they were," he said.
"It's a very new suburb so they'd only just moved in. We didn't even know they had kids until it happened."
He told WAtoday police knocked on his door at midnight and asked what he had heard.
"After the detectives had a chat with us, they said they'd be going all night and they would try to be quiet but it didn't matter... I couldn't sleep anyway.
"It's such a surreal feeling, a very terrible thing to happen."
Police have yet to make any arrests or charges and the investigation continues.