A would-be serial killer and a mother of three with an interest in BDSM have been found guilty of the murder of 18-year-old Aaron Pajich.

Key points: Jemma Lilley and Trudi Lenon found guilty of murdering Aaron Pajich

Jemma Lilley and Trudi Lenon found guilty of murdering Aaron Pajich Prosecutors argued each was equally responsible

Prosecutors argued each was equally responsible Women showed no emotion as verdicts were delivered

Jemma Victoria Lilley, 26, and Trudi Clare Lenon, 43, had been on trial for the past five weeks accused of luring the 18-year-old to their Orelia home in June last year and fatally stabbing him.

His body was found buried under a freshly laid slab of cement that was covered in bright red tiles in the backyard of the home, which was owned by Lilley.

The teenager 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.

A 'cut-throat' defence

Jemma Victoria Lilley (left) and Trudi Clare Lenon had blamed each other for the murder. ( Supplied )

Lilley had never met Mr Pajich, while Lenon had studied with him at a local college. He was also friends with one of her sons.

At the trial, the women mounted what is known as "a cut throat defence" where each blamed the other.

Lilley, who the court heard was obsessed with tattoos, knives, violence and serial killers, maintained she was asleep in another room when Mr Pajich must have been murdered by Lenon.

But Lenon claimed it was Lilley who attacked the teenager with a garotte and a knife as he sat in their home drinking coffee.

Prosecutors argued each was equally responsible, with the court hearing disturbing details of their friendship.

Accused wanted a 'slaughterfest'

That included a series of bizarre Facebook messages, where Lilley called herself "SOS", the main character in a book she had written about serial killers, and Lenon, referred to herself as "Corvina", a character she used when she was a submissive in the BDSM scene.

The messages talked about killing, torture, fear, domination and streets being stained red with the blood of victims.

There was evidence from numerous friends and work colleagues of Lilley, who testified she had told them she wanted to be a serial killer, that she wanted to kill before she was 25 and that she wanted to go on a "slaughterfest".

There was also evidence that in the days while Mr Pajich was missing, Lilley confessed to a colleague in the supermarket where they worked that she had killed someone, divulging details that at that stage only the killer would have known.

A police search of Lilley's home, found a handwritten alphabetical list of torture methods, dozens of knives including a bone saw and scalpels, and a freshly cut out section of carpet, where it is believed Mr Pajich bled after he was murdered.

Lenon had only moved into the house three weeks earlier with two of her young sons, one of whom unknowingly helped Lilley tile over the area where Mr Pajich, who was his friend, was buried.

A composite court sketch of Trudi Lenon (left) and Jemma Lilley during their trial for the murder of Perth teenager Aaron Pajich. ( ABC News )

Killers are 'disgusting animals': mother

The Supreme Court jury deliberated for only two-and-a-half hours before finding both women guilty. They delivered the verdict to a courtroom packed with Mr Pajich's family, detectives who worked on the case and members of Lilley and Lenon's families.

Neither woman showed any emotion as the verdicts were delivered. They were remanded in custody to be sentenced in February 2018 and both face the prospect of life prison sentences.

After the verdicts, Aaron's mother Sharon Pajich said she was happy with the outcome and believed justice had been done.

Ms Pajich said it had been heartbreaking to hear what happened to her son.

"You just can't get it out of your head, it's going to be a lifetime for me.

"He was my precious little boy, my first born, he loved life."

She described Lenon and Lilley as "disgusting animals" and said she hopes they get life sentences.

While thanking the jury for their service, Justice Stephen Hall said that the case had been a disturbing one and counselling was available for any jurors who needed it.