In the coroner's inquest into his death in Auckland District Court this morning, Coroner Gordon Matenga concluded Mr Allen had died of "unnatural causes".
Mr Allen's parents were at the inquest. Mr Allen's mother, Shirley, wept while details of the case were presented, while Mr Allen's father, Mark, called the investigation into his son's death "a farce".
"Why has it taken so long to get to this stage?" he asked. "I have no confidence in any of you."
Coroner Matenga acknowledged the outcome of the inquest had been "most unsatisfactory" for Mr Allen's family.
"The long time it has taken to get to this inquest is regrettable."
However, he said police inquiries had been extensive. "There is no stone which has been left unturned."
Mr Matenga also declared Mr Allen's official date of death would be recorded as September 24, 2009.
So little was known about Mr Allen's death that an accurate time of death wasn't previously recorded. His death certificate says he died on or between September 23 and 24.
Fewer than 10 people were at the house on the night Mr Allen died and police said at the time there were "obvious gaps in honest information" in what those people were telling police.
The house was owned by drug dealer Albert John Rhodes, who was the first person in New Zealand to be sentenced to life imprisonment for manufacturing and supplying methamphetamine.
His brother, Richard, also lived at the house and the pair were jailed in 2009 as part of large-scale drug-ring busted by police in Operation Colossus.