A 25-year-old man pleaded guilty in an Australian court on Wednesday to murdering his three children, wife and mother-in-law in the west coast city of Perth last year.

Anthony Robert Harvey made the plea in an appearance in Stirling Gardens Magistrates Court via video link from prison.

He is to appear at a sentencing hearing in the Western Australia state Supreme Court on June 21. He faces a possible life sentence for each conviction.

The professional gardener killed his wife, Mara Lee Harvey, 41, her 3-year-old daughter Charlotte, and 2-year-old twin sisters Alice and Beatrix in their suburban home on Sept. 3. He then killed 73-year-old Beverley Ann Quinn when she came to visit the next morning.

Harvey stayed in the house for days after the murders before driving 1,400 kilometers (870 miles) north to the mining town of Pannawonica, where he told police on Sept. 9 what he had done.

Police found the bodies of the wife and her mother in the kitchen. The children were found in other rooms.

No explanation for the murders has been submitted to court.

Police said a blunt instrument and knives were used to slay the family.