A teenager has described helping his mother and her housemate lay tiles in the backyard of their "creepy" house where the two women are alleged to have murdered and buried his "excellent friend" Aaron Pajich.

The 13-year-old boy detailed the events in an interview with police recorded about two weeks after his mother, Trudi Lenon, and the woman they were living with, Jemma Lilley, allegedly lured Mr Pajich to their Orelia home in June last year and fatally stabbed him.

The body of the 18-year-old with autism was found eight days later buried under tiles and a slab of concrete.

The boy's interview was played to the Supreme Court in Perth today with him describing Ms Lilley as a "freaky" person who he believed had tried to "groom" him.

The boy said he thought Ms Lilley really liked him, and that if something had happened to his mother she would have wanted him to stay with her.

"She [Ms Lilley] said she didn't feel for anyone but if something happened to me she would be sad ... and she has no emotions she told me."

The boy described the house as "creepy and weird", saying there were dolls from horror movies, including Chucky and Freddy Krueger, and knives on the windowsill.

He also said there were cameras in his room, his little brother's room and his mother's room.

He recalled helping Ms Lilley tile out the back saying he made sure the cats did not get in the way, while she was "making concrete and putting tiles on it".

"My mum helped as well only with the concrete, just making the concrete."

Although he said at one point she felt sick and had to go and lie down.

Jemma Victoria Lilley (left) and Trudi Clare Lenon are accused of murdering Perth teenager Aaron Pajich. ( Supplied )

The boy said around that time his mother seemed scared and he let him and his brother sleep in her room.

"That really shocked me because she never lets me do that," he said.

"I think Jemma scared her sometimes."

He also said Ms Lilley had once tried to "staple" him with a staple gun.

He said the incident happened after he used the word stupid and Ms Lilley told him she hated the word and never to use it in her house.

He said she grabbed a staple gun and went to use it on him but she put it down when he said sorry.

At the start of the interview, the boy was asked if he knew Mr Pajich, to which he responded he used to play video games with him.

He described him as an "excellent friend" who was "very nice to me".

The court heard Ms Lenon knew Mr Pajich because they studied at the same college.

She denied murdering Mr Pajich, but said she helped clean up the scene after Ms Lilley killed him.

Ms Lilley denies any involvement in the teenager's death.