A "have a go hero" who wrestled with an armed thief fleeing the scene of a failed jewellery robbery is being sought by police.
Two men, one armed with a handgun, burst into Harvey Daly jewellers in Long Causeway in Peterborough on Friday morning.
A passer-by tried to stop one of the thieves from getting away.
Detectives said they "need to find him" as they search for the robbers and are appealing for him to come forward.
Pictures of the incident were taken by a passing local photographer.
One of the men was described as white, 6ft (1.8m), in his 20s, with a shaved head.
He was wearing blue jeans and a dark jacket with a grey stripe across the chest.
The second was described as white, aged 20 to 25, wearing a dark blue jacket, blue jeans with the bottoms turned up and black shoes. He had short, dark hair.
Anyone with any information is asked to contact police.