How a serial killer-obsessed woman, and her BDSM-obsessed friend, became murderers.

Jemma Lilley is a 26-year-old from Perth with a fascination with serial killers.

As a tattoo artist and night-fill manager at a local supermarket, Jemma Lilley – according to the ABC – lists motorbikes, horror movies, knives and serial killers as her interests.

She once penned a fictional book where the protagonist was a serial killer called SOS and the head of a murderous cult, and she worshipped figures like horror movie icon Freddy Krueger. Her home was populated with horror movie posters and films and doll figurines.

She had such a curiosity with killers that early last year, she became one.

Her friend, 43-year-old mother-of-three Trudi Lenon, had a festish for bondage. She had been into BDSM sexual practises in the past, her particular experience as a submissive called “Corvina”. It was this experience, a court was told, that shaped her friendship with Lilley. Lenon as the ‘submissive’ of sorts, Lilley as the wannabe killer.

It would drive them, together, to kill an innocent 18-year-old by the name of Aaron Pajich, who loved his family and was an avid computer gamer.

On Wednesday, both women were charged with his June 13 murder.

Aaron Pajich was a good friend of Lenon's 13-year-old son, also attending the same college as the 43-year-old. He was a teen with Aspergers, lured to the house of Lilley under the guise of video games, murdered so violently as if he was a character in one of her horror movies.

"They took advantage of someone who, you know, typically was just looking for friendship, easy to be exploited, not able to read the motivations of other people," Autism advocate Bob Johnson told the media after the verdict.

"He was my precious little boy, he was my first-born ... he was full of life," the victim's mother Sharon Pajich said outside court.

"They (the killers) deserve everything they get for what they've done, they've taken an innocent boy from his loved ones."

His murderers were "disgusting animals" and should never be released, she said.

On the day of June 13, the accused women - who were housemates - targeted and lured the boy to the house. Lenon called him, later testifying she "accidentally" dialled his number, inviting the 18-year-old to meet her and Lilley at Rockingham shopping centre at 9am.

He was dropped off by a friend, farewelling her by saying 'Goodbye and God bless'. It was the last time he was seen alive by family and friends.

CCTV would later catch the accused with Pajich leaving the centre, and an hour and half later, separate security footage from their home would show the three entering Lilley's Perth house around 10.30am.

Lenon said Lilley approached Mr Pajich from behind as he installed games on her computer, garrotted him until the wire broke then stabbed him three times.

Lilley denied everything, taking the stand last week and claiming chilling exchanges between her and Lenon in the lead-up to the murder were research for a book she was writing.

"Profiling techniques will be re-written to accommodate SOS," Lenon wrote, admiringly describing Lilley as a "genuine psychopath of immense control and power".

A video store manager also testified Lilley had said she wanted to kill someone before age 25, and once she had fulfilled murder on her "bucket list", prosecutor James McTaggart said, she was so "full of herself and euphoric", she couldn't help boasting to a work colleague.

Mr McTaggart said she also left incriminating messages to her "obsequious and sycophantic" follower Lenon hours after the killing, saying she was feeling things she had "not felt before".

Though both women blamed the other, it took a jury less than three hours to find them both guilty on Wednesday after a four-and-a-half week trial in an packed courtroom in the Supreme Court of WA.

Jemma Victoria Lilley and Trudi Clare Lenon, they found, killed 18-year-old Aaron Pajich at their Orelia house and buried him in a shallow grave, covering it with concrete and tiles.

The women will face a sentencing hearing on February 23, but Pajich's family will be forever without their son.

 - With AAP.