A man obsessed with serial killers and embracing his "darkness" will spend the rest of his life behind bars for murdering his wife, three children and mother-in-law in a crime a Perth judge said instilled "horror and revulsion".
Anthony Robert Harvey, 25, is the first person in Western Australia ordered by a judge never to be released from prison.
Harvey admitted killing two-year-old twins Alice and Beatrix, three-year-old Charlotte and their mother Mara Lee Harvey, 41, at their Bedford home on September 3, 2018.
Grandmother Beverley Ann Quinn, 73, was murdered when she visited the next morning.
Harvey had written in his journal about "eliminating" his family, despite later telling authorities he loved them and was not angry with them.
"There is no other case that is truly comparable," Justice Stephen Hall told him in the WA Supreme Court on Friday.
"Your actions were so far beyond the bounds of acceptable human conduct that they would instil horror and revulsion into even the most hardened of people."
Justice Hall said the women were unsuspecting, while the children were attacked as they slept, and Harvey carried out the crimes with "apparently calm deliberation".
"This was the place they should have been safest," he said.
"They should have been able to trust their father to protect them. That is the most fundamental duty any parent has.
"You breached that trust and failed in that duty in the most extreme way imaginable."
Some details of Harvey's offending were so shocking they were suppressed.
In Harvey's journal he wrote about embracing his "darkness and animal instincts".
"I am no psycho. I feel. I feel too much, I always have ... I will regret what I do," he wrote.
Justice Hall said the journal entries were "not a mere record of dark fantasies", adding Harvey decided to murder his family one month earlier.
The court heard Ms Quinn and Ms Harvey were struck on the head with a 1.2 metre pipe and repeatedly stabbed with a newly purchased large knife that was almost the size of a machete.
Harvey said he quickly tried to "finish" his wife of three years, stabbing her at least 12 times.
The children were murdered with a smaller knife, with Charlotte stabbed 38 times.
Beatrix was stabbed nine times and Alice 13 times, with both suffering chest and eye injuries.
Justice Hall said there were more wounds than would appear necessary to kill.
They were all photographed with a Polaroid camera, then covered with a doona and flowers, plus notes saying he was sorry and he loved them.
Harvey remained at the house for days and lied to his wife's employer to explain her absence.
He then gathered cash and travelled about 1500km north to Pannawonica where he turned himself in to police on September 9 with the help of his dad.
Harvey, who has no history of violence, described his marriage as good and Ms Quinn as kind.
A psychiatrist suggested Harvey had symptoms consistent with high-functioning autism but could also have a narcissistic personality disorder.
Outside court, Ms Harvey's sister Taryn Tottman said the sentencing was "extremely suitable".
"We ourselves have been given a life sentence, just like the sentence handed out today but with one big difference and that is we did nothing wrong and nor did my family," she said.
Ms Tottman asked that her family be remembered as individuals, including her mother as generous and loving, sister as supportive and determined, Charlotte as enthusiastic, Alice as adventurous and cheeky, and Beatrix for her spirit and hugs.
Police Minister Michelle Roberts said the state government strongly supported Harvey never being released.
"I think he's given up his right to freedom," she told reporters.
Australian Associated Press