WHO gave him those documents? the trail leads to the same place as everything else these days
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Exactly! What was a private doing with access to such info?
His defense is twofold: first, that the information revealed a coverup of a helicopter firing on civilians, and second, that the vast majority of the information is low-level and placed no one in any danger. The latter is common in this sort of case; however, it isn't how intelligence works. Accumulation of enough low-level information can paint a picture that otherwise would be highly classified, including movements of assets, manning, operations planning schedules, etc, etc.
Personally I think Manning is toast. You don't actually have to prove that anyone was killed because of this sort of spying, only that it took place. And that much is pretty much a lock as far as I have seen. The usual disclaimers - I am not an attorney but I did deal with classified information for a lot of years. The rules are crystal clear.