Officers have released a CCTV image of a man in connection with two armed robberies at convenience stores in Peterborough.
The incidents happened in early May in the span of five days are being linked by the police.
The most recent happened at about 2pm on 8 May at AA news in Everdon Way, Westwood.
Three men approached a shop worker and demanded they hand over a cash till. When the victim refused, one of the men pulled out a large kitchen knife.
The offenders attempted to grab the till from the victim but ended up leaving empty handed, stealing bags of sweets on their way out.
The other incident, which is similar, happened at the International Food Shop on Fitzwilliam Street on 3 May.
Anyone who can aid the investigation is asked to contact Cambridgeshire Police on 101 quoting crime reference number 35/27823/21 or online. Alternatively contact Crimestoppers, anonymously, on 0800 555111 or via www.crimestoppers-uk.org.
