Police believe a gun was used by two men who robbed a Ilkeston store.
Two men dressed in black clothing and balaclavas went into the One Stop shop in Charlotte Street, Ilkeston, in the early hours of Thursday, September 11.
The offenders threatened two female members of staff with what appeared to be a black handgun and stole a large amount of cash from the store.
They then tied up the shop workers and left through a rear door which leads onto Grass Street.
Police are appealing for witnesses.
Detective Inspector Donna Sisson, from Ilkeston CID, is leading the investigation.
She said: “The two members of staff were subjected to a terrifying ordeal just as they were preparing to open the shop.
“We urgently need to hear from any witnesses who were in the Charlotte Street or Grass Street areas at the time, who saw suspicious men or vehicles.
“We particularly want to speak to a man who was waiting opposite the shop just after the incident and was picked up by someone in a white flat back van, as we think he may have seen the offenders leaving the scene.”
The robbery took place between 5.20am and 5.35am on Thursday, September 11.
Anyone with information on the robbery should call Derbyshire police on 101, quoting crime reference 38337/14.
Police have reiterated that it is not believed to be connected to another incident that occurred in Charlotte Street around the same time, in which one man died and another was seriously injured.