POLICE investigating the murder of the Nairn banker Alistair Wilson are to check thousands of rounds of ammunition imported into the UK over the last 16 years.
Detectives revealed last year that Mr Wilson, 30, was shot on his doorstep in November, 2004 with a small, German-made handgun using bullets manufactured in the Czech Republic.
On Sunday, one of the officers leading the investigation will fly out to visit the manufacturers of the weapon and ammunition in the hope of narrowing down the list of possible users.
Detective Inspector Gordon Greenlees said: "It seems quite a task but this is a relatively unusual type of ammunition. We are following the audit trail of every single round."
The gun was found by council workmen in a drain ten days after the killing. It did not, however, produce the forensic evidence detectives had hoped would give them the breakthrough in the case.
The .25 calibre weapon is just 4.5 inches long. It was made between 1922 and 1930 by CG Haenel Waffen of Suhl, in what was East Germany. It is believed about 40,000 were made and exported throughout Europe.
The bullets used have been made by Sellier and Bellot from Vlasim, in the Czech Republic, for more than 30 years, and the investigation team has secured records of every round imported into the UK since 1989.
Mr Greenlees said there was only one legal importer in the UK of the type of bullets used in the killing and detectives have already interviewed 109 dealers who have supplied this type of ammunition.
This has led them to identify people who have legally owned Sellier and Bellot ammunition and/or .25 calibre handguns over more than a decade.
It is hoped experts at the munitions factory can narrow the field further by dating the bullets used in the shooting.
Mr Greenlees said the gun could have arrived in the UK in a number of ways - brought back as a trophy, probably after the Second World War, legally imported prior to 1997 when a ban on handguns was introduced, or smuggled into the country.
He said up until 1997 there was a fairly consistent amount of ammunition imported into the UK, but that has dropped off significantly since then.
So far, the investigation has thrown up "some interesting lines of inquiry" about people who held certificates to possess .25 ammunition and have become criminally active.
Mr Wilson, 30, was gunned down on his doorstep by a man wearing a dark jacket and a baseball cap who had called at his home and asked for the banker by name. Despite exhaustive enquiries across the UK and into Europe, the identity of the killer or a motive for the shooting have not been established.