A woman accused of murdering an autistic teenager told a video store manager she wanted to kill someone before she turned 25 and the desire was getting stronger, a court has been told.

Aaron Pajich was found in a shallow grave covered with newly-laid concrete and indoor tiles at the rear of Jemma Victoria Lilley’s Orelia property in June last year, a week after a search was launched for the missing 18-year-old.

Lilley, 26, and her housemate Trudi Clare Lenon, 43, are both accused of murdering Mr Pajich, who was stabbed and garrotted to death.

Camera Icon Accused: Jemma Victoria Lilley and Trudi Clare Lenon.

Angela McKibben told the WA Supreme Court today that Lilley was a customer at her Girrawheen video store on a near daily basis, worked at a nearby tattoo parlour and made the comments around mid-2013.

“She told me that she wanted to kill someone and she wanted to do it before she was 25,” Ms McKibbin said.

After asking Lilley if she really wanted to commit a murder, she allegedly said “yes”.

Camera Icon Buried under concrete: Aaron Pajich. Credit: WA Police

“I said to her ‘it’s pretty hard to get rid of or hide a body’. She said there were a number of ways you could do it.

“She said it was a feeling she had and it was getting stronger, the desire to kill someone.”

Ms McKibbin said Lilley mostly hired movies about serial killers and with horror themes, and her membership password was SOS, which stood for Son of Sam.

The court heard earlier this week Lilley went by the name SOS in text messages with her co-accused and it was also the main character in a book she had written about serial killing.

Ms McKibbin said the comments remained in her mind and she reported them to Crime Stoppers after she saw the case reported in the news last year.

Knife-obsessed Lilley had never met the victim, but he was a close friend of Lenon’s 13-year-old son Christopher, who is expected to give evidence during the five-week trial.