The mafia had no reason to kill police chief Colin Winchester and his death served the organisation no purpose, prosecutors told a jury Monday.
Prosecutor Murugan Thangaraj SC said it was extremely unlikely the mafia was responsible for the murder, and the suggestion they would have done it on the basis of what the informant "You Know Who" told them was laughable.
He said members of the mafia would not be able to cross the street or get a parking ticket in the wake of a hit on Canberra’s most senior officer.
“The last thing these people want is to draw that sort of attention and scrutiny on them,” he said, adding that “they’re there to make money" in their illicit business dealings.
Former treasury official David Harold Eastman, 73, has pleaded not guilty to murdering Mr Winchester on January 10, 1989.
His defence points to what they say is a reasonable possibility the mafia was behind the murder, believing they had been protected by the senior officer in their illegal activities before he appeared to betray them.
On Monday, on what was his fifth day of closing arguments to the ACT Supreme Court jury, Mr Thangaraj moved to dispel the defence suggestion.
The trial has heard Mr Winchester was in charge of an operation in the early 1980s that was observing marijuana growers produce crops near Bungendore with the hopes of gathering intelligence.
At the centre of this operation was an Italian informant, who cannot be identified, who said he had an axe to grind against members of the group.
The informant said he acted as "agent provacateur" and he had got himself into the group, where he encouraged their activites and told them they were under protection from authorities.
Eleven people were eventually charged over the crops.
But Mr Thangaraj said there were serious doubts over the credibility and reliability of the police informant who is said to have connected Mr Winchester to the Bungendore 11.
This was the man police described as duplicitous and underhanded in his dealings with police, he said.
It was fanciful that the mafia would have believed anything he said, Mr Thangaraj said.
Mr Thangaraj said the only time the informant claimed to have mentioned Mr Winchester to the growers was after his murder, and he was trying to get police to look at the same people he was trying to bring down.
Mr Thangaraj said the informant had directly betrayed the mafia yet nothing had happened to him - they had left the traitor alone.
The silk said Mr Winchester had stepped away from the operation in 1982 - years before he was murdered.
He compared that temporal distance from the murder to Mr Eastman, who only weeks before the murder had met with Mr Winchester and days before it had told his doctor he would teach police a lesson.
He told the jury there was no evidence that pointed to the mafia but a mountain of evidence that pointed to Mr Eastman as Mr Winchester's killer.
The prosecutor said it did not take a sharp shooter to shoot someone from close range.
He said it was an amateur that would use a silencer with supersonic ammunition in a high-profile kill.
He referred to the mafia murder of Griffith businessman Donald Mackay and noted it had been executed with a pistol and not a rifle bought locally through the pages of a newspaper.
The trial continues.