THE Central Queensland duo responsible for murdering a young man through a lethal heroin dose left in a letterbox will remain behind bars.
Rockhampton pair Bradley David Hill, 34, and Kerryn Ann Young, 37, were sentenced to life imprisonment after a murder trial in June last year but they tried to argue the verdicts were unreasonable.
Gladstone man Luke McAuliffe, 27, was the victim of jealousy, anger and an intent to kill, the Crown argued during the trial.
The Queensland Court of Appeal, in a judgment handed down on Friday, found there was no miscarriage of justice.
Justice Philip Morrison said there was a substantial body of evidence from which a properly instructed jury could conclude that Hill and Young were guilty of the offences charged.
He said the jury was entitled to reach its guilty verdicts which were not unreasonable or unsupported.
"The essential nature of the case was that Hill delivered a lethal dose of heroin to the deceased, with the aid of Young," he said.
"It is true that there were various discrepancies and inadequacies in the evidence, different recollections of events, different meanings that might be attributed to the evidence and reasons to doubt some of the testimony because of drug-related effects on witnesses, or the passage of time.
"However, the jury, which is the body entrusted with the primary responsibility of determining guilt or innocence, had the considerable advantage of seeing and hearing all the witnesses, and that placed them in the best position to assess where the truth lay.
"In my opinion the various criticisms that have been levelled at the sufficiency and quality of the evidence do not reach the point that the jury's particular advantage is overcome."
Mr McAuliffe was found dead in the bedroom of his mother's Gladstone home on October 10, 2010.
He was good friends with Hill and his on-and-off partner, Young, but there had been a falling out not long before he died.
All three used methamphetamines.
Hill was upset that Mr McAuliffe and Young had been ringing and sending texts pretending they were in a relationship and sleeping together a few nights prior.
The jury heard Hill and Young then colluded to try to trick Mr McAuliffe to come to a motel to "get fried".
When Mr McAuliffe refused, suspecting something was up, Young told him there would be a syringe in the letter box but did not tell him it was heroin or that Hill was delivering it.
Mr McAuliffe, not knowing it was heroin, injected the drug and died shortly afterwards.