An accused murderer confessed she had killed autistic teenager Aaron Pajich to a colleague while they were stacking shelves in a Perth supermarket, and told another she had a "kill type", WA's Supreme Court has been told.
Woolworths employees Matthew Stray and Jeffrey Burling
were giving evidence at the trial of Jemma Lilley, 26, and her housemate, Trudi Lenon, 43, who are accused of murdering the 18-year-old in June last year.
It is alleged the teenager was lured to the pair's Orelia home before being fatally stabbed and buried under tiles and a slab of concrete.
Ms Lilley was Mr Stray's supervisor at Woolworths in Palmyra.
He testified about a conversation he had with her the day he returned to work after a holiday on June 18, last year — five days after Mr Pajich's murder, but three days before his body was discovered.
He said Ms Lilley told him, "I did it. I killed someone."
Mr Stray said he found the information hard to absorb.
"We were working at the time, it was in the supermarket, aisle four," he said.
"I thought 'come on, this has got to be a joke' so I changed the subject."
He said some time passed before she came back to him and detailed what had happened, telling him, "I had to get Trudi to hold him down. I put the wire around his neck and tried to use it and it broke."
Mr Stray also said Ms Lilley showed him a photo of a medieval jester-type character which she said she was going to get as a tattoo "to signify what she had done."
"She said it was like a symbol to represent the significance of killing someone."
He testified she also said "the police were so dumb" and were never going to catch her, and that she sounded excited when she talked about the killing.
He said they had a further conversation in which Ms Lilley showed him a picture of Mr Pajich.
"I think I was getting a bit upset by what I was being told," he said.
"I still could not quite fathom the situation."
"I said to her if this is real and I went to the police, you would be in big trouble.
"She replied 'yeah I know, 25 to life'."
Mr Stray testified Ms Lilley then gave further details about the killing, telling him when the wire broke she grabbed a knife and put it into his chest.
"She said it went in a long way and made cracking sound when it went into his chest," he said.
"She could sense I was getting freaked out and she said 'don't worry Matt they'll all be vigilante-style killings after this'."
He said when he suggested he might have go to the police, she said if he did she would "have to make the problem go away".
Mr Stray told the court he then received a series of text messages from Ms Lilley in which she apologised and described herself as "a good storyteller", saying it was all an act and nothing had happened.
Mr Stray said five days later, after Ms Lilley had been charged with murder, he told police about the conversations.
Another Woolworths employee, Jeffrey Burling, said Ms Lilley told him she wanted to be a serial killer.
Mr Burling said Ms Lilley told him she had a "kill type", and that two other male colleagues were "the sort of person that she would like to kill".
The court heard Ms Lilley referred to herself as "SOS", the main character in a book she had written about a serial killer, and Mr Burling said a few months before Mr Pajich's death, she told him: "SOS was going to come out."
"She wanted to be a serial killer and she wanted to leave her mark," he testified.
Under questioning from Ms Lenon's lawyer, Mr Burling said he did not think Ms Lilley was being serious and he saw it as her seeking attention.