Opening the prosecution case, prosecutor Murugan Thangaraj SC said the murder weapon had the end of its barrel threaded for a silencer and had been offered for sale with a silencer.

But Mr Winchester's wife Gwen heard two shots and found her husband either dead or dying in his car outside their home about 9.15pm on January 10, 1989. He had been shot twice in the head at close range.

Mr Thangaraj said the ammunition used was supersonic, which even with a silencer makes a loud noise.

"The murderer who uses a silencer and supersonic ammunition is not a professional," he said.

The prosecution alleges the murder was committed by former Treasury official David Harold Eastman, 72, who developed a murderous hatred of Mr Winchester who he blamed for imperilling his bid to rejoin the public service.

Eastman had been charged with assault over a scuffle with a neighbour and believed a conviction for violence would bar his re-entry to the public service.

He believed he had experienced injustice as a result of police corruption and pressed for a review of his case in a meeting with Mr Winchester on December 16, 1988.

Mr Thangaraj said there was "basically nil chance" Mr Winchester would intervene and a letter to that effect likely arrived at Eastman's home on January 10, 1989. That night he was murdered.

Eastman has pleaded not guilty. The trial is expected to run for up to six months.

Mr Thangaraj said two spent .22 calibre cartridge cases were found at the murder scene which police determined were fired from a Ruger 10/22 rifle.

The weapon has never been found but information from one witness Raymond Webb pointed to a rifle offered for sale by Queanbeyan man Louis Klarenbeek in January 1989.

Test fired cartridge cases provided by Mr Klarenbeek and another previous owner were matched to those found at the crime scene.

Mr Thangaraj said Eastman, who never held a firearms licence, had made many attempts to buy guns as far back as early 1988.

A Ruger 10/22 he bought from a Canberra man in February 1988 was found in May that year hidden in a culvert under the old Federal Highway.

Mr Thangaraj said it was likely Eastman placed it there as he could not easily take it in and out of his third floor flat.

He said the Klarenbeek rifle was advertised on December 31, 1988 and sold the following day. Mr Webb visited Mr Klarenbeek's home and saw a number of firearms, including a Ruger 10/22 with silencer.

As he departed, he passed another man entering Mr Klarenbeek's home who he later identified as Eastman.

Neighbours reported seeing a man wearing a green jacket and carrying a rifle.

Mr Thangaraj said jurors may have heard suggestions the mafia was behind the murder.

"The mafia would not be buying a gun from a man in Queanbeyan, that was advertised in the Canberra Times and walked down the street with it slung over his shoulder," he said.

The trial continues.

Australian Associated Press