The Royal Newfoundland Constabulary said Monday it believes one person is responsible for a string of armed robberies at convenience stores in St. John's.

One robbery on Sunday evening and two robberies on Monday morning all involved a suspect who threatened staff with a syringe, the RNC said.

Const. Paul Davis said staff at all three incidents provided descriptions that match the same individual.

Davis said the suspect was described as being in his 40s, and slim with dark hair and dark moustache. Davis said the man is between five-foot-three and five-foot-seven in height, and is missing some teeth.

In the first robbery, at a Queens Road store, the thief demanded that the store's attendant turn over cash.

On Monday morning, Davis said, the man fled a store on Hamilton Avenue after an unsuccessful attempt to get cigarettes. Davis said within an hour, he hit up the same Queens Road store for an undisclosed number of cigarettes.