Commutation Because Of Fear ... [Libby] could expose Bush, Chaney and Rumsfeld as war criminals, and destroy the careers of dozens of others in minute

http://andrewsullivan.theatlantic.com/the_daily_dish/2007/07/commutation-bec.html

One aspect of the commutation of Libby's sentence has been overlooked. Libby knows a very great deal about the war crimes of the president and vice-president and even more about the vagaries of the use of WMD intelligence before the war. By commuting his sentence, Bush is obviously trying to ensure that Libby doesn't talk. He is making sure that there's no pressure on Libby to cop a plea and give Fitzgerald more evidence of malfeasance in the White House. A reader explains:

The commutation of this felon's sentence was not a result of arrogance or indifference to the notion of accountability. It was motivated by fear. Libby knows it all, and I mean the whole story. He could expose Bush, Chaney and Rumsfeld as war criminals, and destroy the careers of dozens of others in a matter of minutes. You can be sure that he was told at the outset that he would never see the inside of a jail. The court ruling that packed him off to the slammer immediately triggered the inevitable. It was just a matter of timing.

Another way of seeing this is: obstruction of justice. But, hey, he's the king. According to Addington and Cheney, the president is the justice system.