John Allen Muhammad, the man behind a series of sniper attacks in the US capital in 2002, has been executed by lethal injection.Muhammad, who was 48 and a Gulf-war veteran, went on a shooting spree over a period of three weeks, killing 10 people in random attacks. The shootings terrorised the Washington DC area, with victims shot while shopping, outside schools or just sitting and reading. Eventually he was arrested at a truck stop. Lawyers acting for him claimed the former soldier was mentally ill and suffering from Gulf War Syndrome. Muhammad’s accomplice was Lee Boyd Malvo. He was 17 at the time and is currently serving a life sentence.