Det Insp Bobby Dow, the senior investigating officer, said: ''I appreciate that these people may think that they have nothing that could be of use to ourinquiries, but they were in the area at this particular time and they may have seen something, however irrelevant they believe it to be, that could help us in our efforts to find Mr McMurchie's killer.
"Our internal investigations team are currently conducting inquiries into the incident and we will be re-delivering as much recoverable mail as soon as possible, " he added.