In a statement posted on the WikiLeaks website, he said: "When communicating with the press is 'aiding the enemy' it is the 'general knowledge among the people' itself which has become criminal.
"Just as Bradley Manning is condemned, so too is that spirit of liberty in which America was founded.
"In the end it is not Bradley Manning who is on trial. His trial ended long ago. The defendant now, and for the next 12 weeks, is the United States.
"A runaway military, whose misdeeds have been laid bare, and a secretive government at war with the public. They sit in the docks. We are called to serve as jurists. We must not turn away."
More top news
Labour are to announce new measures they plan to introduce to the NHS if the party wins the General Election.
A teenage racing driver who lost part of both his legs after a horror crash has thanked emergency workers for "saving my life".
The actress plays Rhona Goskirk, who was raped by her new husband on their wedding day in the ITV soap.