A senior British prosecutor has said Gary McKinnon, a hacker wanted in the United States for breaking into military computer systems, will face no further criminal charges in Britain.
"The prospects of a conviction against Mr McKinnon which reflects the full extent of his alleged criminality are not high," Keir Starmer, director of public prosecutions, said.
Starmer said there would have been considerable difficulties in bringing a case against the 46-year-old McKinnon in Britain.
"Most of the witnesses are in the US, as is nearly all the physical evidence and the bulk of the unused material, some of which is sensitive," he said.
British and US authorities had discussed bringing US witnesses and evidence to Britain for a trial, but it was not deemed feasible.
McKinnon, who has Asperger's syndrome, had waged a 10-year legal battle against extradition to the US which finally ended in October when Britain said it would not extradite him because of a high risk he would attempt suicide.
McKinnon's mother Janis Sharp, who has campaigned vigorously for her son, said the news was "wonderful".
"Gary was tearful because of the relief - he was so scared. It's going to be such a nice Christmas not to have everything hanging over us."
She added that she hoped US authorities would now drop their extradition warrant against McKinnon.
Looking for UFOs
McKinnon had admitted accessing US government computers but claimed he was looking for evidence of UFOs.
He was arrested in London in 2002 for hacking into dozens of Pentagon and NASA computers, leaving 300 machines at a naval air station immobilised just after the September 11, 2001 attacks.
He could have faced up to 60 years in a US jail for the breaches, which the US says caused $800,000 worth of damage.
The hacker lost appeals in Britain's House of Lords and the European Court of Human Rights during his decade-long fight.
He was diagnosed in 2007 with Asperger's a form of autism, after an expert on the condition watched him in a television interview and contacted McKinnon's lawyer.
British Interior Minister Theresa May finally rejected US demands to extradite him in October on the grounds that this would breach his human rights as he was "seriously ill", but he still faced possible prosecution in Britain until Friday.