Alistair Wilson would have celebrated his birthday last week

One hundred days on from the shooting, the officer leading the inquiry said recent appeals for specific information had sparked a number of calls.

Detective Chief Inspector Peter MacPhee's team will now place an emphasis on Mr Wilson's earlier years.

Over the coming week officers will be speaking to friends and colleagues from university and elsewhere.

Mr MacPhee promised to sustain the "appropriate levels of resources" until the killer was detected.

He renewed an appeal for information about several unidentified men and vehicles which were seen in the Nairn area on 28 November, the night Mr Wilson was shot on his doorstep.

Detectives are also continuing their inquiries into the murder weapon and further ballistic results are awaited.