<p><br /> A gunman who terrified staff as he carried out the UK's biggest jewellery robbery has been jailed for 23 years.<br /> </p><p><br /> Aman Kassaye planned and executed the heist at Graff Diamonds in Mayfair, central London, last summer.<br /> </p><p><br /> Gems worth up to £40 million were stolen at gunpoint. They have never been recovered.<br /> </p><p><br /> Petra Ehnar, who had been working at the New Bond Street store at the time, told Woolwich Crown Court how she was forced to empty display cabinets with a gun to her back.<br /> </p><p><br /> She was also bundled outside afterwards and told she would be killed if she did not carry out their demands.<br /> </p><p><br /> Kassaye, of no fixed address, used a professional make-up artist to disguise his appearance and a series of getaway cars to escape.<br /> </p><p><br /> He has been jailed for 16 years for conspiracy to rob, a further five years of possessing a firearm and another two years for kidnap.<br /> </p><p><br /> Three other men - Solomun Beyene, 25, of Marylebone, north-west London; Clinton Mogg, 43, of Bournemouth; and Thomas Thomas, 46, of Penrhyn Road, Kingston upon Thames - were each jailed for 16 years after also being convicted of conspiracy to rob.<br /> </p>
