Manning is on trial for giving hundreds of thousands of documents to the secret-spilling website WikiLeaks. He pleaded guilty to charges that could bring 20 years behind bars, but the military has pressed ahead with a court-martial on more serious charges, including aiding the enemy. That charge carries a potential life sentence.
Adrian Lamo, a convicted hacker, said he started chatting online with Manning on May 20, 2010, and alerted law enforcement the next day about the contents of the soldier's messages, including his mention of WikiLeaks founder Julian Assange. He said he continued chatting with Manning on and off for six more days.
On cross-examination, Lamo said Manning never told him he wanted to help the enemy and did not express disloyalty to America.
"At any time, did Pfc. Manning ever say he wanted to help the enemy?" defense attorney David Coombs said.
"Not in those words, no," Lamo said.
Prosecutors have said they will show the 25-year-old Army intelligence analyst effectively put U.S. military secrets into the hands of the enemy, including Osama bin Laden. They said they will present evidence that bin Laden requested and obtained from another al-Qaida member the Afghanistan battlefield reports and State Department cables published by WikiLeaks.
The soldier from Crescent, Okla., has said he did not believe the information would harm the U.S. and he released the information to enlighten the public about the bitter reality of America's wars.
His attorney has also said Manning struggled privately with gender identity early in his tour of duty, when gays couldn't openly serve in the military. Those struggles led Manning to "feel that he needed to do something to make a difference in this world," Coombs said.
Lamo testified Manning had contacted him because of his notoriety in the hacking community and because of his open support and leadership in the lesbian, gay, bisexual and transgender community.
Lamo pleaded guilty in 2004 of computer fraud after he was arrested for hacking the computer networks of the New York Times and Microsoft. He was sentenced to six months house arrest and two years probation.
Manning chose to have his court-martial heard by a judge instead of a jury. It is expected to run all summer. Much of the evidence is classified, which means large portions of the trial are likely to be closed to reporters and the public.
Federal authorities are looking into whether Assange can also be prosecuted. He has been holed up in the Ecuadorean Embassy in London to avoid extradition to Sweden on sex-crimes allegations.
"This is not justice; never could this be justice," Assange said in a statement Monday. "The verdict was ordained long ago. Its function is not to determine questions such as guilt or innocence, or truth or falsehood. It is a public relations exercise, designed to provide the government with an alibi for posterity."
The case is the most high-profile prosecution for the Obama administration, which has been criticized for its crackdown on those who leak information. It's also by far the most voluminous release of classified material in U.S. history, and certainly the most sensational since the 1971 publication of the Pentagon Papers, a secret Defense Department history of U.S. involvement in Vietnam.
The 7,000 pages of the Pentagon Papers showed that the U.S. government repeatedly misled the public about the Vietnam War. Their leak to The New York Times set off an epic clash between the Nixon administration and the press and led to a landmark Supreme Court ruling on the First Amendment.
The material WikiLeaks began publishing in 2010 documented complaints of abuses against Iraqi detainees, a U.S. tally of civilian deaths in Iraq, and America's weak support for the government of Tunisia - a disclosure that Manning supporters said helped trigger the Middle Eastern pro-democracy uprisings known as the Arab Spring.
The Obama administration has said the release of the material threatened to expose valuable military and diplomatic sources and strained America's relations with other governments.