A Perth father who repeatedly stabbed his three young daughters, his partner and her mother had planned the killings for days and made entries in his journal about "eliminating" his family.

Key points: Anthony Harvey killed his three daughters and his wife in their Bedford home

Anthony Harvey killed his three daughters and his wife in their Bedford home He killed his mother-in-law the following day when she arrived at the property

He killed his mother-in-law the following day when she arrived at the property He stayed with the bodies for several days before handing himself in to police

Anthony Robert Harvey, 25, is facing a sentencing hearing in Western Australia's Supreme Court where prosecutors are seeking an order that he "never be released" from custody.

WARNING: This story contains graphic content that some readers may find upsetting

Harvey has pleaded guilty to murdering his 41-year-old wife Mara, their three daughters — three-year-old Charlotte and two-year-old twins Alice and Beatrix — and Ms Harvey's mother, 73-year-old Beverley Quinn.

Their bodies were found in the family's home in Bedford, in Perth's inner north, in September last year.

The court has been told when Ms Harvey returned home from work on the night of September 3, she was hit over the head with a pipe before being repeatedly stabbed.

The children were stabbed in their beds as they slept, with Charlotte suffering 38 stab wounds.

Ms Quinn was murdered the next day when she arrived at the house as usual to help look after the family.

She was hit with the pipe and then repeatedly stabbed.

Beverley Quinn was murdered along with her grandchildren (left to right) Charlotte, Beatrix and Alice. ( Supplied )

When details of the murders were being read to the court, Harvey put his head in his hands and covered his ears.

Crying could be heard from the public gallery, where members of the victim's family were sitting, including Ms Harvey's sister, Taryn Tottman, and her aunt.

Bodies covered with doonas and flowers

The bodies were found covered by doonas and with bunches of flowers on top.

The court heard Ms Harvey's body was found with those of her daughters and placed as though they were "cuddling", surrounded by the children's favourite toys.

Harvey had also bought flowers and put them on top of the doonas.

Handwritten notes to Ms Harvey and Ms Quinn were found near their bodies, in which Harvey said he loved them, he was sorry, that he would do anything to undo what had happened and that he thought he had lost his mind.

Five days after the murders, and after taking money out of the bank accounts he shared with his wife, Harvey drove to the Pilbara town of Pannawonica where his parents lived and confessed his crimes to his father:

"I've done something really wrong … I hurt all of them".

His father then called the police.

'Making family disappear': Journals found in car

A search of his car found photographs of the bodies of the five victims as well as journals written by Harvey, one of which was titled: "This book is intended to explain and document my journey".

The court heard it contained references to life having no reason and meaning.

"I must embrace my darkness and the unthinkable," he wrote. "I am no psycho, I feel too much, I care too much."

Anthony Harvey's journal entries showed he was looking at options to leave his family. ( Facebook: Mara Quinn )

The journals also referred to his "options", including: "leave unannounced", divorce, "making family disappear" and "eliminating family — preps."

WA's Director of Public Prosecutions, Amanda Forrester SC, described the murders as premeditated and well-planned, saying in the 11 days beforehand Harvey sold some of his belongings and bought two knives — including one that was almost the size of a machete.

Ms Forrester also read victim impact statements from Ms Tottman and Ms Harvey's aunt, in which they said their lives had changed forever.

Sorry, this video has expired Family members reveal heartache after Bedford mass killing

'Abhorrent' crimes deserve life in jail: prosecutor

Defence barrister Sam Vandongen SC argued his client should not be subjected to a never to be released order saying while the offences were "almost incomprehensibly and indescribably serious" they did not reach the point of Harvey being locked up for the rest of his life.

The court heard assessments of Harvey suggested he had symptoms consistent with high functioning autism and that he lacked the ability to feel any empathy.

Mr Vandongen highlighted Harvey's relatively young age, his interview with police in which he admitted what he had done, and his guilty pleas as reasons for him not to be given a life term with a fixed minimum period.

However Ms Forrester said Harvey's actions had obliterated an entire family unit.

Mara Harvey's sister, Taryn Tottman, at the Perth Supreme Court with her husband, Alan. ( ABC News: Rebecca Trigger )

"Inexplicable violence was used against people who were entitled to his his protection and his love," she said.

"Any rational, reasonable and informed citizen would say that he has given away the opportunity … the right to ask for a meaningful life outside custody.

"His crimes are so severe … so abhorrent he should expect to be deprived of his liberty for the rest of his days."

Floral tributes were placed outside the house after the bodies were discovered. ( AAP: Richard Wainwright )

Justice Stephen Hall said he would sentence Harvey on July 19.

If Harvey is deemed never to be released, he will become the first person in WA to receive such a sentence since the state's law was changed in 2008.