A detective leading the investigation into a series of robberies at Norwich convenience stores over the past three weeks has today issued a 'we will find you' message to those responsible.

A masked robber escaped with cash from the C and B Sales convenience store in Aylsham Road on Monday after threatening a shop worker with a knife. It was the fourth such incident in just three weeks.

Police are now investigating if the raid was linked to the others across the city this month and Detective Chief Inspector Neil Firm, who is heading up the inquiry, vowed to bring the offender(s) to justice.

Det Chf Insp Firm, who said he was keeping an 'open mind' as to whether the incidents had been committed by the same person, said: 'The message is to whoever's doing this: we will find you, it's only a matter of time. Give yourself up because we will find you.'

Monday's robbery happened just yards from the scene of another crime, on July 9 at the Aylsham Road Convenience Store, when a masked robber produced a knife from his sock and held it against a shop worker's throat, before grabbing tobacco and cash from the till.

A shop on Silver Street in the north of Norwich was raided on July 15, when the robber used a knife to steal money.

And on Monday last week, Reds in St Benedicts Street was targeted, though the suspect fled without any money and was chased by a customer when the alarm was triggered.

Det Chf Insp Firm, who revealed a large number of officers were involved in the investigation, said police would be increasing patrols in the areas which have been targeted to provide reassurance, but he also urged shopkeepers to be vigilant.

He appealed for anyone with information to contact police but warned members of the public not to tackle the offender(s) in person.

Anyone with Information should call police on 101.