In 2002, Gary McKinnon was arrested by the UK's national high-tech crime unit, after being accused of hacking into Nasa and the US military computer networks.
He says he spent two years looking for photographic evidence of alien spacecraft and advanced power technology.
America now wants to put him on trial, and if tried there he could face 60 years behind bars.
Banned from using the internet, Gary spoke to Click presenter Spencer Kelly to tell his side of the story, ahead of his extradition hearing on Wednesday, 10 May.
Click here to Read the full interview ...