There was a "compelling hypothesis" that a now-dead mafia figure was responsible for the National Crime Authority bombing and not Domenic Perre, a court has been told.
Perre has launched an appeal over his jailing for the deadly 1994 Adelaide attack with defence counsel Andrew Tokley KC arguing his convictions were unreasonable and could not be supported on the evidence.
He said there was no direct evidence of Perre acquiring materials to construct the parcel bomb or of having built the device that exploded in the NCA office.
Mr Tokley said an independent assessment of the sufficiency and quality of all evidence would show the conviction was unsafe for a raft of reasons.
He also told the court that trial judge Justice Kevin Nicholson, who sat without a jury, had failed to properly consider the alternative hypothesis that Perre was innocent, including the possibility that someone else had built and sent the bomb, notably former organised crime figure Bruno Romeo.
Also known as The Fox, Mr Romeo, who died in 2016, had been linked to a number of cannabis growing operations and was jailed for 10 years over a crop in Western Australia.
"It is our submission that there exists evidence led by the Crown of a compelling hypothesis consistent with the innocence of the appellant," Mr Tokley told the Court of Appeal on Thursday.
"It is that the bomb was made by a man called Romeo, Bruno Romeo."
Mr Tokley said had that been properly taken into account, Justice Nicholson would have had to return a not guilty verdict.
He said the evidence against Romeo came from "police sources" and not "outlier witnesses".
Mr Tokley also said it should take into account the disadvantage suffered by the defence because of the passage of time, which also meant a number of important witnesses had died.
Perre, 65, did not attend Thursday's hearing due to ill health.
He was previously noted to be suffering from a range of medical issues, including a heart condition and diabetes.
He was jailed for life in October last year after Justice Nicholson found him guilty of the murder of Detective Sergeant Geoffrey Bowen and the attempted murder of lawyer Peter Wallis.
Sgt Bowen died at the scene from extensive injuries, including the loss of his left arm, when the parcel bomb built and sent by Perre exploded in his office.
Mr Wallis, who was standing nearby, lost an eye and suffered severe burns in the blast.
He died in 2018.
Prosecutors argued the bombing was a personal attack on Sgt Bowen stemming from the seizure of a multi-million dollar cannabis crop in the Northern Territory in August 1993.
But in closing submissions, defence counsel Gilbert Aitken said SA detectives had tunnel vision during the entire 27-year investigation and believed only Perre had the motive to make and send the bomb.
In his sentencing remarks Justice Nicolson said the murder of Sgt Bowen and the bombing were "violent, barbaric, and ruthless".
"Your conduct was brutish. That is totally devoid of any human sensibility," he told Perre.
"It was not just premeditated but intricately devised and planned over a lengthy period of time and was executed in cold blood."
If his conviction stands, Perre will be in his mid-90s before becoming eligible for parole, and given his health issues, will likely die in prison.
