James Patrick Roughan, 28, has pleaded not guilty in the Supreme Court in Brisbane to murdering 17-year-old Morgan Jay Shepherd on March 29, 2005.
Instead, he pleaded guilty to a charge of accessory to murder after the fact, but the crown rejected the plea and is proceeding with a murder trial.
Roughan also pleaded guilty to one count of interfering with a corpse.
Mr Shepherd's headless body was found in a shallow grave near Dayboro, west of Brisbane, on April 1, 2005.
The court was today told the teenager died after being stabbed more than 133 times, and that his head had been sawn off.
Prosecutor David Meredith told the court Roughan and his friend, Christopher Clark Jones, 24, had murdered Mr Shepherd after becoming embroiled in an argument during a drinking session at Roughan's home in Sandgate, north of Brisbane.
In his opening address, Mr Meredith told the jury several witnesses would testify that they overheard Jones and Roughan boasting about the killing.
He said one witness would say Jones spoke of holding Mr Shepherd down and stomping on him several times before both he and Roughan stabbed him with a knife.
Mr Meredith said Jones also told friends that Roughan used the head like a puppet and a bowling ball, which Roughan denied.
The court was told the pair enlisted a friend to help dispose of the body, and that they later drove back to Dayboro to bury the body more carefully.
Three people have already been sentenced for helping to dispose of the corpse.
Mr Meredith said Roughan and Jones blamed each other for the "thrill kill", but that "both of them were equally involved" in the death.
He said the "barbaric" killing appeared to have had no motive, but may have been fuelled by the consumption of alcohol.
The trial continues.
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