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Two young women have admitted cold-bloodedly killing a 16-year-old girl because she irritated them.
They dumped Stacey Mitchell's body in a wheelie bin and were still debating the merits of using chainsaws and lime to dispose of her body when they were arrested in Perth days later.
Jessica
Ellen Stasinowsky, 20, and her girlfriend Valerie Paige Parashumti, 19, pleaded guilty to the wilful murder in Perth Magistrates Court.
They killed Stacey Mitchell between December 17 and 21, 2006 while the girl was staying with them at a house in Lathlain in Perth.
Details of the murder emerged during the District Court sentencing in August of David Ross John Haynes, 27, who had pleaded guilty to being an accessary after the fact to the murder, which took place at his father's house.
The evidence was suppressed at the time to avoid prejudicing other cases, but can now be made public following Friday's guilty pleas by the two women.
In the District Court case prosecutor Dave Dempster said both women, Parashumti in particular, had told Haynes that Stacey Mitchell was "pushing their buttons" and they were going to kill her.
Parashumti told Haynes: "No one should destroy your happiness and you should kill anyone who does."
Haynes found her grinding glass in a mortar and pestle and talked her out of putting it Stacey's drink and burying her head in sand to shut her up.
Haynes refused to help trap her but agreed to go to his room and turn the music up after seeing Parashumti with a concrete slab.
"He heard a thud and a lot of movement," Mr Dempster said.
"He heard the deceased, Stacey, yell out, 'help'."
Haynes later became aware Stacey was dead, her body in a wheelie bin.
Over the next few days they all discussed how to get rid of the body, even going to a hardware store to investigate methods of disposal.
"There was something of a shopping list involving things like chainsaws and lime and spades in an effort to see what method could be done," Mr Dempster said.
He indicated the girls may have made a video, saying Haynes was shown footage of Stacey after the event and "there was a great deal of blood around".
On December 21, four days after Stacey was reported missing, Haynes and Parashumti misled police about Stacey's whereabouts.
Later that day all three were arrested and Stacey's body was found in the bin inside a shed.
Chief Judge Antoinette Kennedy sentenced Haynes to two years in jail, backdated to February 16 when he was arrested, saying he was pathologically dependent on the dominant Parashumti. He will be eligible for parole after 12 months.
Parashumti and Stasinowsky will appear in the WA Supreme Court on December 17 ahead of sentencing.
Parashumti also was charged with obstructing police but she did not enter a plea on that charge.
Outside the court, Detective Sergeant Steve Post said the guilty pleas were a good result for Stacey's family.
"Absolutely, police are very happy the family have been spared the ordeal of a trial," he said.
"Make no mistake, this was a cold blooded killing."
- AAP