Graff robbery diamond turns up in Hong Kong pawn shop Graff Diamonds of London, where the diamond that has turned up in Hong Kong was stolen during a 2007 armed robbery. Photograph: Clive Gee/PA A diamond stolen from Graff Diamonds of London in one of the UK's biggest ever jewellery heists has turned up in a Hong Kong pawn shop - and is now being kept under lock and key in New York while the owner sues to get it back. The more than 16-carat yellow diamond has been identified as one of those stolen in a July 2007 hold-up at Graff Diamonds in New Bond Street, Mayfair, according to court papers. Two men stepped out of a Bentley Continental Flying Spur limousine, pretended to be shoppers and chatted up store staff before producing handguns and stealing diamond and gem-studded rings, necklaces, pendants and earrings. Some of the jewellery items reported stolen from Graff Diamonds. Photograph: PA/Metropolitan police The haul was valued at up to £26m ($39m) at the time, though amounts of up to £42m have been given in different reports. If the diamond is from Graff's it would appear to be the first and only piece recovered since the robbery. The Hong Kong shop submitted the diamond for certification to the Gemological Institute of America, according to the lawsuit filed by Graff's at the New York supreme court in Manhattan. The institute turned out to have certified the diamond before the robbery and determined it was the same one, albeit recut. Graff's says it "is and was the true owner of the diamond and entitled to immediate possession of the diamond" but the pawn shop will not let the institute return it. The court papers do not give a value and the company's lawyer did not immediately return a call. There was no answer or voicemail at the Hong Kong shop. The institute said it could not discuss the matter because of the dispute but it regularly worked with police when stones were reported lost or stolen. Four men were eventually convicted over the Graff Diamonds robbery. Aman Kassaye, who planned and executed it, was found guilty of conspiracy to rob, kidnapping and possession of a firearm after a three-month trial at Woolwich crown court in London. He was given 23 years' jail. Solomun Beyene, 25, of London, Clinton Mogg, 43, of Bournemouth, and Thomas Thomas, 46, of Kingston upon Thames were each jailed for 16 years after also being convicted of conspiracy to rob. In 2003 the New Bond Street store was robbed of an estimated £23m worth of gems. A man was convicted of that theft and jailed for 15 years. Various other Graff outlets in London have been targeted in a string of robberies dating back as far as 1980, and a Dubai store was robbed in 2007 - the same year as the London robbery involving the disputed diamond.