I think more likely they wanted to impede justice to support their cronyism.
I also wonder why W has been turning a deaf ear to the previous administration's shenanigans. I do not believe, as you suggest it is to keep their own misdeeds from being exposed. I believe it is simply because he is an ethical gentleman and does not want to be involved with prosecuting his predecessor.
Here on FR, they might call me a Bushbot for that. But there a lot of sleeper DUmmies here with older signup dates.
"I believe it is simply because he is an ethical gentleman and does not want to be involved with prosecuting his predecessor."
Could motivate some things. But a coverup of 9-11?