THE two women convicted of helping each other carry out the brutal “thrill killing” and callous backyard burial of autistic teenager Aaron Pajich-Sweetman have been jailed for life - with both to serve at least 28 years.

Jemma Lilley, 26, and Trudi Lenon, 44, went on trial at WA’s Supreme Court last year accused of fantasising, planning and then executing the murder of the 18 year-old in June 2016, after luring him to the Orelia house they shared.

Over a month of gruesome evidence, the court heard allegations of how Lilley, a young woman obsessed with knives and serial killers, and Lenon – a mother-of-three with a history as a “submissive” in Perth’s BDSM scene – had built a close relationship, referring to each other by ‘pet names’.

Camera Icon A pot with meat and acid which police thought was carried out as an experiment. Credit: Supplied

The pair were jailed for life on Wednesday - with Justice Stephen Hall describing the crime as “morally repugnant”.

It is one of the highest minimum sentences ever handed down by a WA judge.

He said the murder was for the “pitiless pursuit of your own desires ... you killed for your own pleasure.”

Mr Pajich’s parents, senior police, former friends of Lilley and Lenon and dozens of onlookers were in Court to hear the sentence.

Neither women showed any emotion as the sentence was delivered.

Following the sentencing, Aaron’s stepmother Veronica Desmond said she hoped the pair would “rot” during their time in prison.

“And I hope you live to regret what you’ve done,” she added.

When asked how his family was coping, Aaron’s father Keith Sweetman had just one word: “Suffering.”

Disability activist Samantha Connor, who attended the trial daily, said she hoped life would mean life

“The reason the murderers were caught so quickly is that Aaron had people around him that loved and supported him

“Aaron was a trusting man and Jemma Lilley was a narcisstic psychopath.”

Camera Icon The patio where Aaron Pajich-Sweetman was buried. Credit: Supplied

During the trial, the court was told that Ms Lilley referred to herself as SOS – which was also a serial killer character in a book she had written in her teens, and also the name of an American serial killer who had murdered eight victims in the mid 1970s’.

Ms Lenon was known as “Corvina”, a name she had adopted through her participation in bondage and sado-masochistic sex.

The state alleged after the two women met and moved in together, along with Ms Lenon’s younger children, they teamed up to carry out a ‘thrill kill’ on a vulnerable target.

That target was the Mr Pajich-Sweetman, who was known to Ms Lenon through a shared attendance at a Kwinana college and his friendship with her teenage son Cameron.

The 18 year-old was also on the autism spectrum, and according to prosecutors, “still inhabited a child’s world”, including a passionate interest in computer games.

It was that interest which the court heard prompted Ms Lenon to lure Mr Pajich to the Orelia house she shared with the 26-year-old Ms Lilley, who worked as a night fill manager at Woolworth’s in Palmyra.

Mr Pajich-Sweetman was first garrotted before being stabbed twice in the neck and once in the chest.

Camera Icon Trudi Lenon and Jemma Lilley the day before the murder buying acid at Bunnings. Credit: Supplied

The court also heard how both women shared the planning for the murder – including chilling trips to Bunnings the day before the murder.

Those trips were to buy 100 litres of hydrochloric acid, which prosecutors said had been intended to help dispose of a body.

A large pot in the garage of the home showed evidence that some type of meat had been dissolved with acid.

But ultimately, after he was killed, Mr Pajich-Sweetman was buried, under concrete also bought at Bunnings around the time, along with the tiles purchased from a Rockingham salvage shop.

Prosecutor James McTaggart said the killing was done so that Ms Lilley could feel the "euphoria" of murder – and the exhilaration was so intense she allegedly confessed what she had done to a workmate, a boast the prosecutor said she wore as “some sort of badge of honour”.

Material from the women’s phones, extracted after they were arrested, also showed the ‘sub/dom’ relationship between the pair through a series of Facebook messages

The first of which showed Ms Lenon, 43, writing to Ms Lilley, 26, to say: "I will fear you but respect you … I see you as my dominant".

A separate message from Ms Lilley to Ms Lenon said: "My mind is the darkest being you will ever be laying your life in the hands of".

A text hours after Mr Pajich-Sweetman was stabbed to death, from Ms Lilley's phone, read: “I am seeing things I haven’s seen before, and feeling things I haven’t felt before. It is incredibly empowering, these images — thank you”.

Ms Lenon allegedly replied “You are welcome SOS” — referring to the persona that Ms Lilley referred to herself as, which was also the name of the central character in a book she had written about a serial killer.

Analysis of both women’s phones revealed the day after the alleged murder, Ms Lenon searched for the website of the National Missing Person Co-ordination Centre, and then the wikipedia page “Life imprisonment in Australia”.

Ms Lilley’s phone contained searches including the words “slit throat”, the court heard.

Since the verdict, Lenon has been attacked in prison with boiling water, with the court told that had meant she had been placed in a protected area of the prison, with authorities fearful she could be attacked again.