Police saw Colin Winchester's Italian informant as a golden opportunity to infiltrate the mafia in Australia in a way no one had before, the David Eastman trial heard Wednesday.
Without Mr Winchester's operation, law enforcement officials would not have known what they did about the Honorata's structure, business dealings and finances, the senior NSW officer said.
The operation was headed by Mr Winchester, who was then in the early 1980s a detective superintendent in the Australian Federal Police working in Canberra.
His informant would supervise the members of the Italian mafia grow crops while holding out that they were under some kind of protection by people in authority.
The informant eventually helped lead to the people responsible for the murder of Donald Mackay, a Griffith businessman, the court heard.
David Eastman's defence team lead further evidence of Mr Winchester's operation as its case drew to a close on Wednesday.
Mr Eastman has pleaded not guilty to the January 10, 1989 murder of Mr Winchester, who was at the time the assistant commissioner of police in Canberra.
Mr Winchester was shot twice in the head as he got out of his car at home in Deakin.
The defence have pointed to an alternative theory that someone within the Italian mafia orchestrated the hit on the senior police officer.
Mr Winchester's Operation Seville went for several years before three men connected to Mr Winchester's operation were arrested in Melbourne.
Detective Sergeant John Weel said in a statement read to the jury by a barrister that he had tailed the men in a gold Mercedes and a blue Ford sedan travelling south from Canberra to Melbourne.
He arrested them outside Melbourne and they were charged with conspiring to sell and traffic cannabis.
In his statement the officer said he spoke with Mr Winchester about the ACT officer's desire not to mention Canberra in an upcoming court appearance - to keep the pressure off his informant.
He said he later heard from a reliable source that two of the men had been planning to bribe him with $30,000 each to withhold evidence.
It later came to be that detective Weel met Mr Winchester's informant at the University Cafe in Melbourne's Lygon Street, while under audio and visual observation.
He said the informant told him he was under political pressure.
The informant said two of the arrested men had $30,000 to give the officer and both the informant and the officer would get a bullet if he could not satisfy those involved.
At a later date, one of the arrested men who said he was making his own enquiries, something should happen in the next day or so.
The officer met his seniors and they decided to withdraw the charges.
But after more discussions, and the understanding that the informant was not affected by the Victorian arrests, a second version of Operation Seville was started, senior NSW officer Bob Blissett said in a statement.
Mr Blissett, who held the rank of superintendent and was in charge of the Bureau of Criminal Intelligence in the 1980s said in his statement that Mr Winchester had approached him about the operation, given the plantations would take place in NSW.
The NSW police approved of the plan, he said in the statement read to court, which would endeavour to infiltrate the Honorata and its members, and their involvement in organised crime.
It was a "golden opportunity to infiltrate this organisation, which no one had be able to do so before".
Without Operation Seville, he said, authorities would not have known what they did about the Honorata's structure, business dealings and finances.
The statements of the former police officers read to the court by the defence drew to a close the defence case and the evidence to be lead during the trial.
The trial has heard from more than 127 live witnesses and 41 witnesses who had either died or were too unwell to attend court, and whose statements or evidence were read to the court.
Acting Justice Murray Kellam told the jury they would reconvene the court on Wednesday, October 3 to hear the Crown's closing arguments.
The trial continues.