A 25-year-old Perth man who murdered five members of his family, including his three young daughters, has become the first person in WA to be jailed for life with an order he never be released from prison.

Key points: Anthony Harvey killed his family in a Perth home with knives and blunt instruments

Anthony Harvey killed his family in a Perth home with knives and blunt instruments He stayed in the house with the bodies for five days after the attacks

He stayed in the house with the bodies for five days after the attacks He then turned himself in at a remote police station in WA's Pilbara

Anthony Robert Harvey admitted responsibility for what is one of WA's worst mass killings — the murders of his 41-year-old wife Mara, their daughters Charlotte, three, and two-year-old twins Alice and Beatrix, and their grandmother Beverley Quinn, 73.

They were all killed at the family's Bedford home in September last year, with the Supreme Court told Harvey had planned the crimes for days and written in a journal about eliminating his family.

Justice Stephen Hall sentenced Harvey to life on Friday, saying "there is no other case that is truly comparable".

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

Harvey stabbed to death his wife Mara (left), their three children and Mara's mother. ( Facebook: Mara Quinn )

Harvey stayed in house with bodies

Mara Harvey was the first to die — she was hit with a piece of pipe when she returned home from her night fill job at a local Coles supermarket and was then stabbed.

Harvey then targeted his daughters, who were stabbed while they were sleeping, with one suffering 38 wounds.

Beverley Quinn and family (from left to right) Charlotte, Beatrix and Alice were murdered in September 2018. ( Supplied )

The next morning, when Ms Quinn turned up as usual to help look after the family, she was hit with the pipe and then stabbed.

Harvey stayed in the house for five days with the bodies, which he photographed after covering them with blankets and bunches of flowers.

Ms Harvey's body had been moved to the children's bedroom, where he said he had arranged the bodies to appear as though she was cuddling the girls, whose favourite toys he placed around them.

He wrote letters to the victims, saying he loved them, he was sorry and that he had lost his mind.

Harvey then sold some of his belongings as well as some women's jewellery and he withdrew money from his wife's bank account before driving to the Pilbara town of Pannawonica, where his parents lived.

Once there he confessed his crimes to his father.

"I've done something really wrong Dad … I hurt them all of them," he said.

Harvey's father immediately called the police.

At his sentencing hearing last month, prosecutors argued the murders were so serious Harvey had forfeited any right to a life outside jail.

Harvey and his wife Mara ran a lawnmowing business together before the attack. ( News Video )

But his lawyers said their client's young age, his pleas of guilty and his prospects for rehabilitation meant he should receive a life jail sentence, with a fixed minimum term.

No words adequate to convey magnitude of offences: Judge

Justice Hall said the order to never be released — the maximum penalty available under WA law — was reserved for the very worst cases.

"Frankly, I struggle to find words that are adequate to convey the magnitude of your offences," he said.

"Your actions are so far beyond the bounds of acceptable human conduct that they instil horror and revulsion into even the most hardened of people.

"It is necessary to make an order that you never be released in order to meet the community's interest in punishment and deterrence."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 13 seconds 3 m 13 s Anthony Harvey is sentenced to never be released from jail

Justice Hall said Harvey took the lives of his family members in an "exceedingly brutal manner".

He said they were all loving and much loved, and the children in particular were "so very young".

"Their potential to grow and achieve and have families of their own was cut short by your actions," he said.

"The murder of children is conduct that is held by society to be especially heinous."

Anthony Harvey will never walk free from jail after the harshest sentence handed down in WA history. ( ABC News )

Justice Hall said the children were asleep in their beds, where they "should have been safest".

"They should have been able to trust their father to protect them," he said.

"That is the most fundamental duty any parent has.

"You breached that trust and failed in that duty in the most extreme way imaginable."

Harvey was impassive throughout the sentencing.

A life sentence for killer and family

Mara Harvey's sister, Taryn Tottman, read a statement outside court, describing the sentence as "extremely suitable".

"In an ideal world, now that sentencing has been handed down, my family would return," she said.

"But I know that this will never happen.

Mara Harvey's sister Taryn Tottman (centre), said the "never to be released" order was extremely suitable. ( ABC News: Dave Weber )

"Instead, we ourselves have been given a life sentence.

"Just like the sentence handed out today but with one big difference — and that is that we did nothing wrong and nor did my family."

She asked that her family members not be known for how they died, but for who they were.

"Please remember my mum, Beverley, as a generous, committed, loving mum and friend that she was," she said.

"My sister, Mara, for her love, support and determination.

Mara Harvey was the first of the family to be attacked by her husband. ( Supplied: Facebook )

"My nieces, Charlotte for her enthusiasm and laughter, Alice for her sense of adventure and cheekiness, and Beatrix for her spirit and, of course, her hugs."

She said she wanted to thank police, forensic investigators, detectives and prosecutors, and everyone involved in the case.

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

The harshest sentence ever handed down

No other person in WA has ever received a "never to be released" sentence — a provision that was introduced under changes to the state's homicide laws in 2008 by the then Labor government.

Before that, the only person who faced the possibility of never being released was William Patrick Mitchell, who murdered four members of one family with an axe in the Mid West town of Greenough in 1993.

William Patrick Mitchell was sentenced to life for murdering Karen MacKenzie and her three children. ( ABC News )

At one point there was an order that he should never be granted parole, but it was overturned on appeal.

He was then given a life term with a 20-year minimum, which expired in 2013. He applied for release on parole but was refused.

Under the legislation, offenders are eligible to be considered for parole every three years after they have completed their term.

Mitchell's applications have always been refused.

He is next due for parole consideration in September this year.