Police have warned shop workers to be “extra vigilant” after three robberies in Northampton were linked.
Officers said staff were threatened with weapons during the thefts at Tesco, in Duston, on Tuesday and at Morrisons, in Kingsthorpe, and Subway, in Mereway, on Wednesday.
It said in each incident two men stole cash and alcohol or cigarettes, leaving staff unhurt but “shaken”.
Det Insp Hayley Thurston said: “We are in the early days of investigating these incidents, but due to the similarities in what has happened we are linking them. We’re urging shop workers to remain vigilant, especially at the start and end of each day, and to please report any suspicious behaviour to us.”