A firearms expert said cartridges found at the scene of Colin Winchester's murder matched those found in Victoria and Captains Flat.
The evidence links the murder to a Ruger 10/22 purchased and then sold on by Queanbeyan gun seller Louis Klarenbeek.
Prosecutors say the murder weapon was the same Ruger 10/22 Mr Klarenbeek allegedly sold to accused killer, David Harold Eastman, on January 1, 1989, for $250.
However, Mr Klarenbeek, now deceased, failed to identify Mr Eastman as the buyer.
Mr Eastman, 72, is on trial in the ACT Supreme Court accused of shooting Mr Winchester twice in the head after he pulled into his neighbour’s Deakin driveway.
Mr Eastman has pleaded not guilty.
The court has previously heard that the alleged murder weapon had been originally owned by Fynus Caldwell, who had fired it at a reserve near Woodside in Victoria.
He later gave the weapon to a Canberra gun smith, Noel King, to sell on commission.
It is believed Mr King then sold the rifle to Mr Klarenbeek for about $200.
The court has heard that Mr Klarenbeek had test fired the weapon at a Captains Flat Road quarry.
Mr Klarenbeek later retrieved spent cartridges from the quarry, three of which he said were from the Ruger.
Cartridges said to have been fired from the rifle were also retrieved from Woodside.
Police located two spent bullet cartridges lying on the grassy strip alongside Mr Winchester's car, where the police chief had been found slumped dead in the driver’s seat.
Australian Federal Police forensic firearms expert Christiaan Pieterse compared the cartridges found at the crime scene, with those discovered in Captains Flat and Woodside, in Victoria.
Mr Pieterse told the court on Thursday that unique markings from the firing pin indicated the cartridges had been fired from the same rifle.
Mr Pieterse, under cross-examination, was questioned about possible limitations in not having the firearm to test alongside the cartridges.
He told the court the presence of the rifle would not have changed his conclusions.