Pfc. Bradley Manning told a judge on Thursday that he sent the information to enlighten the public about American foreign and military policy. Manning said he didn't think releasing the information would harm the United States.
"I believed that if the general public, especially the American public, had access to the information ... this could spark a domestic debate on the role of the military and our foreign policy in general," Manning said. He said he was troubled by counterinsurgency strategies that seemed to ignore "the complex dynamics of the people living in the environment."
He also said he spilled the secrets to the anti-secrecy website WikiLeaks to expose the American military's "bloodlust" in Iraq and Afghanistan.
The 25-year-old Oklahoma native pleaded guilty in the case. Now, military judge Col. Denise Lind is weighing whether to accept Manning's guilty plea to reduced charges on 10 counts.
Even then, military prosecutors can still pursue a court-martial on the remaining 12 charges. One of those is aiding the enemy, which carries a possible life sentence. Prosecutors haven't disclosed their plans.
Manning admitted to sending hundreds of thousands of Iraq and Afghanistan battlefield reports, State Department diplomatic cables, other classified records and two battlefield video clips to WikiLeaks in 2009 and 2010 while working as an intelligence analyst in Baghdad.
He said he first sent the battlefield reports to The Washington Post and The New York Times. He said he felt a reporter at the Post didn't take him seriously, and a message he left for news tips at the Times was not returned. That's when he sent them to WikiLeaks.
Manning pointed out one particular combat video in 2007, where an aerial assault by a U.S. helicopter killed 11 men, including a Reuters news photographer and his driver. The Pentagon concluded the troops mistook the camera equipment for weapons.
"The most alarming aspect of the video to me was the seemingly delightful bloodlust the aerial weapons team happened to have," Manning said, adding that the soldiers' actions "seemed similar to a child torturing ants with a magnifying glass."
As for the sensitive State Department cables, he said they "documented backdoor deals and criminality that didn't reflect the so-called leader of the free world."
"I thought these cables were a prime example of the need for a more open diplomacy," Manning said. "I believed that these cables would not damage the United States. However, I believed these cables would be embarrassing."
The Obama administration has said releasing the information threatened valuable military and diplomatic sources and strained America's relations with other governments. The administration has aggressively pursued individuals accused of leaking classified material, and Manning's is the highest-profile case.
The Associated Press contributed to this report.