On the opening day of Manning's court martial in Fort Meade, Md., military prosecutors accused the 25-year-old Oklahoman of being responsible for what they've described as the biggest leak of classified information in American history.
They opened their case against him by describing Manning's motive in providing military secrets to "the enemy," and noted that some of that information was later found in Osama bin Laden's Pakistani hideout after the 9-11 mastermind was killed by U.S. forces in May 2011.
Manning "used his military training to gain the notoriety he craved," Capt. Joe Morrow said in his opening statement to the court martial proceedings.
"This is a case about a soldier who systematically harvested hundreds of thousands of classified documents and dumped them onto the Internet, into the hands of the enemy — material he knew, based on his training, would put the lives of fellow soldiers at risk."
Manning, who worked as an intelligence analyst for the military, has confessed to giving hundreds of thousands of sensitive documents to the anti-secrecy website WikiLeaks.
In a pre-trial hearing in February, Manning said in a statement that he had passed on information that "upset" or "disturbed" him, but denied providing WikiLeaks with anything he thought would put the United States in danger if it were to become public.
"I believed if the public was aware of the data, it would start a public debate of the wars," he said.
Prosecutors, however, have upped the ante, alleging that Manning violated the federal Espionage Act and aided "the enemy," a crime that carries a potential life sentence. Manning has pleaded not guilty to that charge.
Twice as many people have been prosecuted under the 1917 Espionage Act under U.S. President Barack Obama than in all previous administrations combined.
Obama's White House has also been the most zealous in contemporary U.S. history in pursuing those it suspects of leaking information to the media. Attorney General Eric Holder is currently on the hot seat for the Justice Department's attempts to seize the phone records and emails of reporters working on national security stories.
Prosecutors in Fort Meade said they planned to delve into chat logs they insist prove that Manning and WikiLeaks founder Julian Assange conspired to get the information into the public domain. WikiLeaks has never said whether Manning was the source of its information.
Manning was first detained in May 2010 for leaking a video that showed a cockpit video from a U.S. Apache helicopter firing on civilians and journalists in Baghdad. In his February statement, Manning said he initially contacted the Washington Post and the New York Times to offer the video, and they expressed no interest.
The video later showed up on WikiLeaks.
Throughout much of his three-year detainment, Manning has been kept in harsh military detention, including several months in solitary confinement. The top torture expert at the United Nations called it "cruel and degrading" treatment.
Manning's ordeal has also served, in part, to turn him into a martyr. He's become a hero to many, including Daniel Ellsberg, the former Defense Department official who leaked the so-called Pentagon Papers in 1969 to the New York Times.
Ellsberg's actions showed the U.S. government had lied to the public about the Vietnam War, and helped turn public opinion against the conflict.
"I have a considerable identification with whistle-blowers, but Bradley above all because it is the first time in 40 years since the Pentagon Papers that someone has put out a large raft of material," Ellsberg said in a recent interview.
"And therefore he does deserve to be, I believe, seen as a hero .... I hope that I would have done in the digital age just what he did. He did it exactly right."
On Saturday, Manning's supporters, including Ellsberg, rallied outside Fort Meade, near Baltimore.
"People came from great distances to stand with a true American hero," said Jeff Paterson, director of the Bradley Manning Support Network.
Manning's lawyer, David Coombs, thanked the public for its support in a statement released on the eve of the court martial. He said Manning's supporters have brought "worldwide attention to this important case."
In court on Monday, Coombs described Manning as being "young, naive but good-intentioned," adding his client took pains to ensure that none of the documents he was leaking would cause harm.
The documents on the conflicts in Iraq and Afghanistan, Coombs argued, were "low-level field reports" that "did not discuss huge operations, did not contain the names of intelligence sources."
"He was selective," Coombs said. "And he released these documents because he was hoping to make the world a better place."