An onlooker may have crucial information about a robbery in a tunnel near a Northampton car showroom.
The incident happened in Rothersthorpe Road between 2.30pm and 2.40pm last Wednesday (May 3).
The victim was walking through a tunnel at the back of Crystal Motors when he was jumped on from behind by two men who dragged him to the floor and stole his bag.
The first was white, skinny and aged about 18, a police spokeswoman said. He was wearing a Nike baseball cap and a black North Face gilet.
The second was white, aged about 18 and wearing a full balaclava and black tracksuit.
It is understood that a witness was in the tunnel at the time, who Northamptonshire Police would like to trace.
Anyone with information should call Northamptonshire Police on 101 or call Crimestoppers, in confidence, on 0800 555111.