Detectives have released an e-fit of a man suspected of committing two robberies in Brighton and Hove and another in Worthing.
The most recent robbery happened on Tuesday (16 August) at Replay Exchange in Western Road, Brighton.
The suspect entered the shop armed with a hammer at about 9.25am just as the shop manager was opening up and ordered him to get down on the floor.
He then jumped over the counter and grabbed several iPhones before making off in the direction of Churchill Square on what is described as a BMX-style bike.
The Replay Exchange robbery is being linked to a similar incident in Hove on Saturday 13 July.
At about 12.30pm the suspect walked into the Carphone Warehouse in George Street.
He threatened staff and used a pair of wire cutters to remove two mobile phones from the display before riding off on a bicycle.
The Worthing robbery happened on Thursday 7 July at the Carphone Warehouse in Montague Street.
The manager was opening up the shop at about 9am when the suspect entered the store.
He threatened staff with a knife before stealing two mobile phones and riding off on a bicycle up Montague Street.
Detective Constable Scott Moore, from Brighton and Hove CID, said: “Due to the times of the robberies and the modus operandi we believe all three may have been committed by the same man.
“Fortunately, no staff were injured but it is nonetheless a frightening experience and all three shops have lost thousands of pounds worth of phones.
“Officers are conducting house to house inquiries and speaking to local businesses.
“We would like to advise mobile phone premises to please be alert when opening up in the morning.
“Dial 999 immediately if you see anyone acting suspiciously.”
The suspect is described as a black man, about 5ft 5in to 5ft 7in tall, in his late teens to mid twenties, of thin build with very dark skin and short black hair.
During the Brighton robbery the suspect had two shaved lines on the left-hand side of his head.
In the Worthing robbery he was sporting a distinctive “chin-strap” beard and thin moustache.
In the Hove robbery the suspect was wearing a grey hoodie, jeans, black trainers and a dark blue backpack.
During the Worthing robbery he was wearing a light grey woolly zip up jumper, possibly with darker grey fur lining the hood, baggy light blue jeans and trainers.
He was also wearing a Russian-style winter hat which had grey fur at the forehead and ear flaps and tan-coloured fabric covering the head.
Sussex Police said that it would like to hear from anyone who has information about the suspect or who has been offered mobile phones for sale.
Witnesses should call Sussex Police on 0845 6070999 or the independent charity Crimestoppers anonymously on 0800 555111.
