(CNN) -- The father of Bradley Manning, the soldier responsible for the largest leak of classified information in U.S. history, says he believes his son didn't do it.
He doesn't see how he could have done it, Brian Manning told CNN's Anderson Cooper 360 in an interview that aired Tuesday night.
"Logistically, I can't understand -- because knowing computers as well as I do -- how you could get that much data out of a room with three other people in there, you know, sitting in close proximity, where everybody could see what everybody was doing," he said.
"I can't understand how that could be done."
His son, a former Army intelligence analyst, was convicted last month of stealing and sending a trove of classified data to the website WikiLeaks.
He was acquitted of the most serious charge he faced, aiding the enemy, which could have put Manning in prison for life without the possibility of parole.
Now, he faces a maximum possible sentence of 90 years.
When he entered guilty pleas on the lesser charges this year, Manning spent more than an hour in court reading a statement about why he had leaked the information.
He said that the information he distributed "upset" or "disturbed" him, but none of it, he thought, would harm the United States if it became public.
"I believed that if the general public, especially the American public, had access to the information ... it could spark a domestic debate on the role of the military and our foreign policy in general as it related to Iraq and Afghanistan," Manning said, according to a statement from his lawyer.
Asked about those comments, Brian Manning said that he thought his son was posturing.
"Yeah, I think he was grandstanding," he told CNN, adding that if his son was, in fact, responsible for the leak, he had no excuse for his actions.
"I mean, I can't fathom any reason to myself why he should be -- that I should forgive him for doing something like that because it's against my creed, or code of honor," he said.
Brian Manning alluded to his time in the military, saying that he never spoke about what he did and wished his son had the same character.
Authorities say the younger Manning delivered three-quarters of a million pages of classified documents and videos to the secret-sharing site WikiLeaks, which 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.
"It's my country as well, and leaking information that's going to damage my country, and the soldiers in our military, you know, that would be very upsetting," Brian Manning said.
CNN's Chelsea J. Carter, Ashley Fantz and Larry Shaughnessy contributed to this report.
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