Police surveillance of David Harold Eastman when investigating the killing of Canberra's police chief crossed the line and became harassment, his lawyers told the jury in his murder trial on Wednesday.
After more than a day hearing from prosecutors who allege Mr Eastman, 73, shot Australian Federal Police Assistant Commissioner Colin Winchester in his car on January 10, 1989, it was the turn of his barristers to begin mounting a defence.
They raised the spectre of Mafia involvement in the killing, in a move that again caused the trial to be briefly closed to the public.
Barrister George Georgiou SC said the former public servant made a "full and vigorous denial of the charge of murder".
He said Mr Eastman also denied saying that he wanted to kill Mr Winchester, denied buying a Ruger 10/22 rifle from Louis Klarenbeek, and denied trying to sell that rifle to Denis Reid.
Other threats allegedly made by Mr Eastman about police before Mr Winchester's death were - if said - expressions of frustration, he said.
"It is disputed and it is in issue that they reflected a murderous intent," Mr Georgiou said.
The trial earlier heard allegations Mr Eastman wanted to kill the "bastard police" and that he told his doctor they should be taught a lesson.
“Even if they were said – [the words] 'police should be taught a lesson' – fall far short of demonstrating an intention to kill Mr Winchester."
Prosecutors earlier in the trial alleged police bugs hidden in Mr Eastman's flat caught him after the shooting whispering "He was the first man I ever killed" and "I had to kill him sitting down".
Mr Georgiou said the jury members would need to decide for themselves if the covertly recorded mutterings of Mr Eastman were in fact confessions.
“The potential for error is high is when it comes to interpreting what is on those tapes," Mr Georgiou said.
The silk also asked the jury to consider the tapes in the context of Mr Eastman's life at the time and his admitted "unhappy dealings" with police.
"The surveillance crossed the line and became harassment to Mr Eastman," the defence barrister told the jury.
Mr Georgiou also challenged the Crown's theory about Mr Eastman's motive to kill Mr Winchester.
The Crown had pointed to a hatred of police and fear that a potential criminal conviction over an altercation with a neighbour would have stopped him returning to the public service.
"The prosecution theory is strongly disputed. The alleged motive is strongly disputed," he said.
“Such a theory ignores Mr Eastman's history of pursuing his rights."
Mr Georgiou challenged whether a conviction meant Mr Eastman would never return to work.
Even the meeting with Mr Winchester in a bid to have the charge dropped was not the "end of the line", he said, as the senior police officer had informed Mr Eastman it was a question for the Director of Public Prosecutions.
There was no issue Mr Eastman was keen to return to the public service, nor that he had a strong sense of grievance, Mr Georgiou told the jury. But he reminded them Mr Eastman had in December 1988 been ruled fit to return, albeit with restrictions.
The extent the restrictions on his return would hinder Mr Eastman getting a job was unknown, the barrister said, but it was strongly in dispute that they were "significant".
The court was again closed briefly as Mr Georgiou raised the spectre of Mafia involvement in the killing during his hour-long opening address.
It had closed briefly on Tuesday when the prosecution premptively rebutted the suggestion.
"As a matter of logic, if Mr Eastman did not kill Mr Winchester someone else did," Mr Georgiou said when the court reopened to the public and media on Wednesday.
"The defence does not have to prove who it was, however, on this case there is evidence that points to a reasonable possibility that Mr Winchester was killed by someone involved with, associated with or recruited by the Mafia."
After the defence opening, prosecutors began a process of tendering documentary evidence on Mr Eastman's dealings with the public service.
The trial continues.