Story highlights WikiLeaks founder Julian Assange calls Bradley Manning a hero

If found guilty of aiding the enemy, Manning could be sentenced to life in prison

He is accused of releasing 750,000 pages of classified documents and videos

After spending three years in custody, the man accused of the largest leak of classified information in U.S. history will learn Tuesday whether he has been found guilty of aiding the enemy.

A verdict from the judge in the court-martial of Pfc. Bradley Manning will be announced at 1 p.m. ET Tuesday, according to a spokeswoman for the military district of Washington.

If found guilty on the aiding the enemy charge, Manning could be sentenced to life in prison. He has pleaded guilty to nearly a dozen lesser charges that carry a sentence of up to 20 years behind bars.

Whether Manning is a whistle-blower or a traitor who betrayed his country has been hotly debated.

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Authorities have accused Manning of delivering three quarters of a million pages of classified documents and videos to the secret-sharing site WikiLeaks -- which has never confirmed the soldier was the source of its information. The material covered numerous aspects of U.S. military strategy in Iraq, gave what some called a ground view of events in the Afghanistan war and revealed the inner workings of U.S. State Department diplomacy in leaked cables.

When he entered his guilty pleas on the lesser charges earlier this year, Manning spent more than an hour in court reading a statement about why he leaked the information.

He said the information he passed on "upset" or "disturbed" him, but there was nothing he thought would harm the United States if it became public. Manning said he thought the documents were old and the situations they referred to had changed or ended.

"I believed if the public was aware of the data, it would start a public debate of the wars," he said during his court-martial. He said he was "depressed about the situation there," meaning Iraq, where he was stationed as an intelligence analyst.

He first tried to give the information to The Washington Post, but a reporter there didn't seem like she took him seriously, he said. He left a voice mail for the New York Times and sent an e-mail to the newspaper but, he claims, he didn't hear back. So he decided to give the information to WikiLeaks.

After WikiLeaks published a trove of documents related to the Afghanistan war in 2010, the site became an international sensation, as did its chief, Julian Assange.

"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 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. Assange has said he thinks the claims against him are Washington's way of getting him arrested so that he can be extradited to the United States to face charges.