A terrified Tesco worker was threatened at knifepoint by a robber who helped himself to cash from the till on Monday.
The stocky thief, aged about 30, walked into the Tesco Express store at Greenleys local centre at 1.50pm, say police.
Wearing a dark coloured coat and hat, he threatened a member of staff with a knife.
It is believed the offender lives locally and police are connecting him to a similar robbery at a store in Conniburrow last month.
On February 22 the offender went into the Sirajico Mini Market at 2.20pm and pushed aside a member of staff who was opening the till to take a payment.
The crook grabbed cash from the till and fled.
Police are now appealing for witnesses of either incident and urging anybody who knows the thief to come forward.
Information can be given to Detective Constable Lucy Jarrett or Detective Constable Leanne Shepherd by dialling 101.
Anybody who does not want to talk to the police can contact Crimestoppers anonymously on 0800 555 111 or online at www.crimestoppers-uk.org