He left a voice mail for The New York Times and sent an e-mail to the newspaper but, he says, he didn't hear back.
So, he said, he decided to give the information to WikiLeaks.
At some point, according to a California hacker Adrian Lamo, who says he communicated via instant messaging with Manning, the soldier confessed to possessing sensitive documents.
Shortly after alleged messages between Manning and Lamo were published in 2010, Lamo spoke to CNN.
He said he turned Manning in to authorities. His reason?
"... it seemed incomprehensible that someone could leak that massive amount of data and not have it endanger human life," Lamo said. "If I had acted for my own comfort and convenience and sat on my hands with that information, and I had endangered national security ... I would have been the worst kind of coward."
As Manning's court case dragged on, in December 2011 his defense argued that the military didn't heed warning signs that the soldier was falling apart mentally.
A few months before Manning was arrested, Army command referred him to a psychologist for evaluation because he appeared to be "under considerable stress" and "did not appear to have any social support system and seemed hypersensitive to any criticism" and "was potentially a danger to himself and others."
WikiLeaks, Assange and Manning
Manning was arrested within months of a video that appeared on WikiLeaks in April 2010. The secrets-busting site called it "Collateral Murder." It appeared to be shot from a U.S. Apache helicopter as it fired on a group of people in Baghdad in 2007. A dozen people were killed; among them were a Reuters TV news cameraman and his driver.
The video showed that Reuters' Saeed Chmagh survived an initial strafing by the helicopter, but apparently died when it opened fire again -- this time on people attempting to get him off the sidewalk where he lay and to move him into a van.
The footage quickly made news, elevating what was once virtually unknown WikiLeaks to a globally recognized name. Later, a U.S. investigation into the attack found that the crew mistook the journalists' cameras for weapons while seeking out insurgents who had been firing at American troops in the area.
But, according to court documents and testimony, by the time the world saw the video, Manning had already downloaded hundreds of thousands of classified documents and videos.
Within months, the soldier had been accused of using his computer skills to commit what the government called treason.
While Manning sat behind bars, WikiLeaks and its chief Julian Assange became household names.
WikiLeaks published a trove of documents related to the Afghanistan war in 2010 and followed that with a headline-making document dump about the Iraq war and then another release of diplomatic messages by U.S. State Department diplomats.
"We call those types of people that are willing to risk ... being a martyr for all the rest of us, we call those people heroes," Assange has told CNN's Jake Tapper. "Bradley Manning is a hero."
Assange described the case against Manning, specifically the aiding the enemy charge, as a serious attack against investigative journalism.
"It will be the end, essentially, of national security journalism in the United States," he said on the eve of the verdict.
Assange spoke from the Ecuadorean Embassy in London. He sought refuge there to avoid extradition to Sweden, where he is wanted for questioning over allegations of sex crimes.