There is an ongoing military investigation. I'm sure that military prosecutors are evaluating Manning's liability beyond what he's already been charged with, specifically to see if he might qualify for the additional charge of Art. 106a-Espionage, which of course carries with it the possibility of a death sentence.
For several reasons, military prosecutors as well of the chain of command (to include the President and his subordinates), don't make public pronouncements with respect to criminal investigations. Why? Because of something known as Unlawful Command Influence (UCI), which can be grounds for reversal on appeal.
However, the Congress is not tethered by such legal constraint. They can investigate, and say whatever they wish without jeopardizing Manning's prosecution. I'm sure when the new Congress is installed, this will be the first order of business as far as hearings are concerned.
What needs to be realized is that the leaking of info will become a way of life. It’s the digital age of LATERAL CONNECTIVITY, the death of heirarchical top down control apparats and the birth of a new form of democracy in which the DATA will be allowed to speak for itself, freed from any interpretive spin. Buckle up kids, it’s time for a little sentient personal autonomy. Blow the whistle yourself, nobody higher up will...