A would-be serial killer and a mother-of-three with an interest in BDSM have been sentenced to life with a 28-year minimum for the calculated murder of Perth teenager Aaron Pajich.

In June 2016, Jemma Victoria Lilley, 26, and Trudi Clare Lenon, 44, lured the 18-year-old to the southern suburbs home they called "Elm Street" — after the cult horror movie series A Nightmare on Elm Street — and fatally attacked him with a knife.

His body was found buried in the backyard of the property on Broughton Way, Orelia under a freshly laid slab of cement that was covered in bright red tiles.

Mr Pajich, who had signs of autism, had two stab wounds to his neck and one to his chest, as well as an injury on his neck consistent with him being attacked with a garotte.

He also had defensive wounds on his hands, the court heard.

Justice Stephen Hall said it was likely, due to the nature of the wounds, that "death came quickly" to Mr Pajich.

While he had never met Lilley, Lenon was his study colleague and the mother of a friend with whom he liked to play computer games.

Police charged the women a day after Mr Pajich's body was discovered.

A section of freshly laid paving in the backyard of Jemma Lilley's house, where Aaron Pajich's body was buried. ( Supplied: Supreme Court of WA )

In his sentencing remarks, Justice Hall said while it was not clear who had delivered the fatal injuries to Mr Pajich, he held both women accountable for what he termed a "morally repugnant" crime.

"You are both equally responsible … there can be no doubt the both of you intended to kill Mr Pajich," he said.

Justice Stephen Hall sentences Jemma Lilley and Trudi Lenon for the murder of Aaron Pajich. ( Supplied )

Justice Hall said messages exchanged by the two women showed they had no remorse for their actions, including Lilley's message to Lenon the day after the killing that she felt "incredibly empowered".

"There is nothing to suggest either of you had the slightest regret about what you had done," Justice Hall said.

"You both derived malicious pleasure from the suffering of Mr Pajich's family."

As members of his family packed the public gallery, the court was told Lilley maintains her innocence and intends to lodge an appeal.

Aaron Pajich's stepmother Veronica Desmond speaks to the media outside court. ( ABC News: Samuel Yang )

Mr Pajich's mother, father and stepmother all welcomed the sentence but said nothing would bring him back.

His stepmother, Veronica Desmond, said she said she hoped the two women would "rot," but also that they would live to regret what they had done.

Disturbing details during trial

The pair both denied murdering Mr Pajich and blamed each other, but they were found guilty by a Supreme Court jury in October last year.

Sorry, this video has expired CCTV footage shows Trudi Lenon holding knife around the time Aaron Pajich was killed

The trial, which lasted five weeks, was told the two had developed a sinister friendship, with Lilley adopting the persona of "SOS" — the main character in a book she had written about serial killers.

Jemma Victoria Lilley (left) and Trudi Clare Lenon received a life prison sentence for murdering Aaron Pajich. ( Supplied )

Lenon played the role of "Corvina" — a "sycophantic submissive" character she had used when she was into BDSM.

The women exchanged a series of disturbing messages in which they talked about "SOS's first kill", torture, a "screaming, pleading victim" and bloodstained streets.

The final exchange appeared to be just a few days before Mr Pajich's death.

The jury deliberated for only two-and-a-half hours before delivering its verdict.

New Year's Day prison attack

The women had been held in Bandyup Women's Prison since their conviction last year, and Lenon has twice been targeted in attacks from other inmates.

The first was after her arrest and involved hot water, but she did not require hospitalisation at that time.

Lenon was then attacked a second time on January 1, when a 35-year-old inmate allegedly poured a container of boiling water over her.

She was taken to Fiona Stanley Hospital with serious burns. Her lawyer said she ended up spending three weeks in hospital, including time in the intensive care unit.

There were no physical signs of injury on her when she appeared in court on Wednesday.

The inmate who allegedly carried out the attack was charged with two counts of causing bodily harm.