Mr Wilson was gunned down on the doorstep of his home

Witnesses, whom police know were in the area of Alistair Wilson's home after his murder, are being asked to offer a mouth swab for DNA testing.

They will be compared to unidentified DNA samples which were recovered during forensic examinations of the area.

Mr Wilson, 30, was gunned down on the doorstep of his home in November.

Detective Chief Inspector Peter MacPhee, in charge of the murder hunt, has promised the samples will be destroyed once the murder has been solved.

He said the tests were being carried out in order to eliminate people from the investigation.

Rewards offered

Two months after the shooting, the inquiry team has yet to find a motive for the killing.

The suspect was described as being aged 35 to 40 and was wearing a baseball cap and a dark blouson jacket.

Detectives in December confirmed that a handgun found in a drain near the scene was the murder weapon.

Police hunting Mr Wilson's killer are to carry out DNA tests

Police have been following up a number of calls after the case was featured on the BBC's Crimewatch programme.

Crimestoppers has offered �10,000 for anyone with information leading to the capture of the killer and a national newspaper has offered a similar reward.

Mr Wilson's widow, Veronica, has told how her life and that of her two young sons had been "torn apart" by her husband's murder.