An extradition treaty between the US and Britain makes the legal case cut and dried: Gary McKinnon of North London in the UK hacked his way into US military and space agency computers in the days after 11 September 2001 and he must be tried in the US. McKinnon, 43, has admitted to the actions, but says he was simply looking for information on UFOs. Beyond the legal issue is a human rights debate over whether or not McKinnon, who has Asperger’s syndrome (the high-functioning end of the autism range) should be extradited and tried for a crime that could put him in prison for the rest of his life. The man’s family has pleaded with the British home secretary, Alan Johnson, to intervene but Thursday the family received a letter from him saying he is powerless. Legal advice differs on his ability to stop the extradition.