FORT MEADE, Md. (AP) — Pfc. Bradley Manning went on trial Monday for leaking hundreds of thousands of classified documents to the anti-secrecy website WikiLeaks, including sensitive information prosecutors said fell into enemy hands.

Manning, a 25-year-old former intelligence analyst from Oklahoma, has admitted to giving troves of information to WikiLeaks in the biggest leak of classified information in U.S. history, but military prosecutors want to prove Manning he also aided the enemy, which carries a potential life sentence. They said they will present evidence that former al-Qaida leader Osama bin Laden asked for and received information WikiLeaks published.

"This is a case of about what happens when arrogance meets access to sensitive information," Capt. Joe Morrow said in his opening statement.

Manning's supporters hail him as a whistleblowing hero and political prisoner. Others say he is a traitor who endangered lives and national security.

"This, your honor, this is a case about a soldier who systematically harvested hundreds of thousands of documents from classified databases and then dumped that information on to the Internet into the hands of the enemy," Morrow said.

Defense attorney David Coombs said Manning was "young, naive, but good-intentioned." Coombs said Manning selectively leaked material he believed could make the world a better place, mentioning an unclassified video of a 2007 U.S. Apache helicopter attack that killed civilians, including a Reuters photographer.

"He believed this information showed how we value human life. He was troubled by that. He believed that if the American public saw it, they too would be troubled," Coombs said.

In his dress blue uniform and wire-rimmed eye glasses, the slightly built Manning followed a slide show of the prosecutor's hour-long opening statement, watching on a laptop computer at the defense table. The slide show also was projected on three larger screens in the small court room, which only had seating for about 50 people.

Later, almost motionless, the soldier sat forward in his chair, looking toward Coombs throughout the defense attorney's 25-minute opening statement, which focused on what Coombs said was Manning's struggle to do the right thing as "a humanist" concerned about the war.

Manning has said he did not believe the information would harm the U.S. Coombs did not address whether bin Laden ever saw any of the material Manning leaked.

Manning chose to have his court-martial heard by a judge instead of a jury. It is expected to run all summer.

Manning was arrested in Iraq more than three years ago. Since then, he admitted to sending the material WikiLeaks and pleaded guilty to reduced charges on nine counts that alleged violations of federal espionage and computer fraud laws, and to one count alleging violation of a military regulation prohibiting wrongful storage of classified information. The maximum for those offenses is 20 years in prison.

But Manning admitted guilt without a deal from the U.S. military who wanted to pursue more serious charges.

It's the most high-profile case for an Obama administration that has come under criticism for its crackdown on leakers. The six prosecutions since Obama took office is more than in all other presidencies combined.

In February, Manning told military judge Army Col. Denise Lind he leaked the material to expose the American military's "bloodlust" and disregard for human life in Iraq and Afghanistan.

U.S. officials have said the more than 700,000 Iraq and Afghanistan battlefield reports and State Department cables sent to WikiLeaks endangered lives and national security.

Within two weeks of his arrival in Iraq in late 2009, Manning began downloading information, seeking out WikiLeaks and communicating with the website's founder, Julian Assange, despite warnings from the military, the prosecutor said.

"The evidence will show that Pfc. Manning knew the dangers of unauthorized disclosures to an organization like WikiLeaks and he ignored those dangers," Morrow said.

The material WikiLeaks began publishing in 2010 documented complaints of Iraqi detainee abuses; a U.S. tally of civilian deaths in Iraq; and America's weak support for the government of Tunisia — a disclosure Manning supporters said encouraged the popular uprising that ousted the Tunisian president in 2011 and helped trigger the Middle Eastern pro-democracy uprisings known as the Arab Spring.

The release of the cables and video embarrassed the U.S. and its allies. The Obama administration has said it threatened valuable military and diplomatic sources and strained America's relations with other governments.

Coombs contended Manning chose information he knew would not identify diplomatic or intelligence sources by name.

Much of the evidence is classified, which means large portions of the trial are likely to be closed to reporters and the public.

The court-martial's high degree of secrecy, including refusals to promptly release even routine filings and rulings, has fueled protests by Manning supporters, including documentary filmmaker Michael Moore, musician Graham Nash, actor John Cusack and Pentagon Papers leaker Daniel Ellsberg.

Ellsberg, a former military analyst, has said Manning's disclosures may be more significant than his own leak of a top-secret history of the Vietnam War expansion in 1971.

About 20 Manning supporters demonstrated in the rain outside the visitor gate at Fort Meade. They waved signs reading "free Bradley Manning" and "protect the truth" while chanting "What do want? Free Bradley. When do we want it? Now."

Lind previously ruled Manning had been illegally punished by being held in a military brig alone in a windowless cell 23 hours a day, sometimes with no clothing. She said he should get 112 days off any prison sentence he receives.

Manning has said he corresponded online with someone he believed to be Assange but never confirmed the person's identity. Assange is the subject of a separate federal investigation into whether he can be prosecuted for publishing the information Manning leaked.

WikiLeaks has been careful never to confirm or deny Manning was the source of the documents.

Assange has been holed up in the Ecuadorean Embassy in London to avoid extradition to Sweden on sex-crimes allegations.