Within months, Manning was behind bars, accused of using his computer skills to commit what the government called treason.
From Oklahoma to Iraq
It was a far cry from his beginnings.
Hailing from the small Oklahoma town of Crescent, population less than 1,300, he was a gearhead with a love of computer games and a passion for current events, his friends and family told CNN in 2011.
After working a series of part-time jobs and, at one point, living out of his car, he joined the Army in 2007.
But it was a tough acclimation, his friends later said, in large part because of the military's "don't ask, don't tell" policy. According to friends and his own writings on the Internet, Manning is openly gay.
Then, in 2009, Manning deployed to Iraq.
He was at Forward Operating Base Hammer in southeast Baghdad, where he worked as an analyst reviewing possible threats to U.S. troops.
According to Fein, the prosecutor, within two weeks of his arrival in Iraq, Manning began working with WikiLeaks founder Julian Assange over what to leak and how to do it.
Assange has taken refuge at the Ecuadorean Embassy in London to avoid extradition to Sweden to face questioning in sex-crimes allegations, charges he claims are a ruse by allies of Washington to arrest him and then extradite him to the United States to face charges.
Manning spent hours at work during off-hours downloading documents, Fein said.
Manning, the prosecutor said, was well aware of the military's policy about divulging classified material and the repercussions of doing it. The soldier had even taught classes about protecting the material, Fein said.
"Manning had no allegiance to the United States," Fein told the court last week, adding that he was "not a whistle-blower; he was a traitor."
But Manning's attorney offered another picture, one in which the war deeply affected his client.
It began, his attorney told the court, after an attack on a convoy with his comrades. A roadside bomb exploded beneath a car full of civilians that had pulled aside to let the military vehicles pass.
Although members of his 305th Military Intelligence Battalion were not hurt, Coombs said, at least one civilian was killed. That changed Manning's outlook on the war, his lawyer said. He "struggled."
He was further disturbed by the "Collateral Murder" video, the attorney said.
"Did they all deserve to die? That is what Pfc. Manning is seeing when he watches this," Coombs told the judge after playing the video in court.
It was for those reasons, according to Coombs, that Manning then started selecting information to reveal, believing that it would be better if it were public.
Coombs said his client was selective in the information he diverted from a controlled-access computer system where he worked as an "all source" intelligence analyst.