A Western Australian father has admitted to killing his wife, mother-in-law and three daughters in September last year.

Anthony Robert Harvey pleaded guilty via video link to five counts of murder today at Stirling Gardens Magistrates Court in Perth.

The guilty plea comes after the 25-year-old handed himself into police on the morning of September 9.

Harvey allegedly used knives and blunt instruments to murder his wife and children on September 3 before killing his mother-in-law the next day in the kitchen of the family home in Bedford, in Perth’s inner east.

The bodies of his 41-year-old wife Mara Harvey, three-year-old daughter Charlotte, two-year-old twins Beatrix and Alice, and mother-in-law Beverley Quinn, 73, were found in a Bedford house on the same day he handed himself into police.

Mrs Harvey was murdered soon after finishing a night shift at Coles.

Beverley Quinn with her grandchildren (from left to right): Charlotte, Beatrix and Alice. Photo / Supplied

Police said Harvey, who ran a Jim’s Mowing franchise, stayed in the house for days after the murders before travelling about 1500km north to the remote town of Pannawonica where he handed himself in.

Jim’s Group managing director Jim Penman said Harvey had been a respected and well-liked franchisee.

“(He) had given no hint of financial or emotional problems in the many contacts we had with him over the past few months,” Mr Penman said.

“The only suggestion of trouble was his failure on several occasions to respond to phone calls.”

Last year the family of the deceased released a statement via police saying they were heartbroken and described Mrs Harvey as a loving mum.

“Mara loved being a mum and she loved her girls. She was so proud of each of them and was doing a great job of raising them. Her girls were her world,” her sister Taryn said.

“Charlotte was an energetic, bubbly confident little girl who loved people and loved socialising. Alice was outgoing, adventurous and cheeky, while Beatrix was at times a little bit more quiet but gave the biggest hugs.”

She said there were “no words to explain the emptiness and loss that we are feeling”.

She also described their mother Beverley as a kind-hearted, caring mother and grandmother who was always there for her family.

Distraught neighbours also spoke about the family and how they hadn’t been seen in recent days. The street, normally filled with the laughter of the three girls, had been eerily quiet.

Nearby neighbour Doug Roberston told news.com.au he often heard the girls playing.

“Who would want to hurt little children?” Mr Robertson said. “I just don’t understand it.”

“I didn’t see the kids but I could hear them playing. I just can’t believe this has happened.”

During an earlier court appearance last year, Ms Quinn’s grieving sister Wendy Frost broke down outside court crying “why would you kill babies?”

Her oldest sister Maureen Devereux said the family had not seen the tragedy coming before they got a phone call from Taryn.

“All I could say was why? We sit all day, morning to night talking about it,” Ms Devereux said. “I am very angry and want to know why.”

Brother-in-law Alan Tottman said what happened was “unfathomable”.

“It’s just a very raw time,” he said. “We can’t come to terms with what’s happened, we don’t know why it’s happened. There was no indication of trouble, problems.”

Harvey will face a sentencing hearing in the West Australian Supreme Court on June 21.