An armed robbery at a Kettering bookmakers on Thursday night is being linked to several more which have taken place in the county in the last nine days.
Four betting shops have been hit since February 13 and police say there have been similarities in the way the robberies were carried out and in the descriptions offered by staff.
On Thursday night, police scrambled the force helicopter after a robbery at the BetFred branch in Dalkeith Place, Kettering.
However, according to the helicopter log, they crew were not able to trace the suspect.
That incident followed three other robberies. The first happened at Ladbrokes, in Midland Road, Wellingborough, on Wednesday, February 13, at about 6.30pm.
Two then took place in Northampton on Saturday, February 16, at BetFred in Kettering Road at 6.20pm and Ladbrokes in Fish Street at 7pm.
Det Insp Ali Reynolds said: “There are similarities in the way the crimes were carried out in all four robberies and the description of the offender is the same - a black man, of stocky build, between 5ft 5in and 5ft 9in and in his twenties.
“We would like to speak with anyone who saw anything they feel may be relevant around the times of the robberies or anyone who witnesses anything suspicious in the future.”
Witnesses to these incidents, or anyone with information, should call Northamptonshire Police on 101 - alternatively, information can be given anonymously to Crimestoppers on 0800 555 111.