Campaigners in the US will stage two days of rallies ahead of the trial of Bradley Manning, the US soldier hailed as a brave whistleblower by some and condemned as a traitor by others after he leaked more than 250,000 pages of military secrets to the website Wikileaks.
Private Manning has pleaded guilty to 10 lesser charges of passing on information, which would carry a maximum sentence of 20 years in prison.
But he faces 12 further charges, including aiding the enemy, for which he could face life in prison, in a military trial which begins on Monday 3 June and is likely to continue until mid-August.
Julian Assange, the WikiLeaks founder, will monitor the trial closely from the Ecuadorean Embassy in London, where he has sought sanctuary from British police wanting to extradite him to Sweden over allegations of sexual assault.
Manning is expected to mount a public interest defence, accusing the US military of "bloodlust" in a pre-trial statement referring to military incident reports he leaked, included an infamous "collateral murder video" depicting civilians being gunned down by an attack helicopter in Baghdad.
"The most alarming aspect of the video to me was the seemingly delightful bloodlust they appeared to have," Manning said in the statement.
"They dehumanised the individuals they were engaging and seemed to not value human life by referring to them as 'dead bastards' and congratulating each other on the ability to kill in large numbers."
He said the leaked reports "represented the on-the-ground reality of both the conflicts in Iraq and Afghanistan", adding: "I felt that we were risking so much for people that seemed unwilling to cooperate with us, leading to frustration and anger on both sides.
"I began to become depressed with the situation that we found ourselves increasingly mired in year after year."
Referring to the cache of State Department cables - the largest leak of classified US documents in history - Manning said: "The more I read, the more I was fascinated by the way that we dealt with other nations and organisations.
"I also began to think that the documented backdoor deals and seemingly criminal activity didn't seem characteristic of the de facto leader of the free world."
Freedom of speech campaigner Daniel Ellsberg, who leaked the Pentagon Papers exposing government secrets over Vietnam to the New York Times in 1971, will address campaigners gathered outside Fort Meade in Maryland, where the trial will take place.
The prosecution argues that Manning communicated with the enemy as the cables would have been accessible to al Qaeda via the Wikileaks website.
Prosecutors are expected call a witness from the US Navy Seals unit that killed Osama bin Laden. He is expected to testify that he seized digitised WikiLeaks documents during the raid, showing the terror group benefited from the leaks.
Opinion is divided. Floyd Abrams and Yochai Benkler, prominent defenders of the First Amendment enshrining freedom of speech, said a guilty verdict on the contested charges would leave media outlets open to prosecution for publishing future leaks.
"The extreme charges remaining in this case create a severe threat to future whistleblowers... We cannot allow our concerns about terrorism to turn us into a country where communicating with the press can be prosecuted as a capital offence," they wrote in the New York Times.
But Walter Pincus, the Pulitzer-prizewinning journalist, countered that revealing sensitive information should be regarding as simple lawbreaking.
Major General John Altenburg, an expert in US military justice, said simply proving that America's enemies had accessed the information was not enough to secure a conviction on the espionage charges. The prosecution must prove Manning had reason to believe publishing the disclosure would harm the US, he said.
The trial will increase pressure on US president Barack Obama after it was revealed that the US Justice Department secretly obtained the phone records of up to 100 Associated Press reporters.
Manning has chosen to forgo a jury in the trial, which will be presided over by Colonel Denise Lind, the chief judge of the Army's 1st Judicial Circuit. That decision led to speculation that his lawyers felt a military jury could be hostile to their client, regarding him as a traitor.
"A private first class does not get to decide whether a conversation between a high-level US official and the king of a Gulf nation should be made public," said PJ Crowley, the State Department spokesman who resigned after criticising the military's treatment of Manning in custody.
US authorities were accused of torture after putting Manning on "extreme suicide watch", meaning he was held in solitary confinement, kept in his cell for 23 hours a day, had all possessions withheld. and was held overnight under lights and repeatedly stripped of his clothes.
Click below to watch the 'collateral murder' video leaked by Bradley Manning.