Where do we draw the line?

After reading the news this morning, I was thinking about my previous post re: prosecution of Bush officials. I was reading two articles about a recent press conference held by Ken Salazar, the new Secretary of the Interior.

Salazar pledges to clean up the waste and fraud that has beset that department for years. Yes, even before the Bush Administration. But in the last eight years, that department has really become a scandal heap. (Does the name Abramoff ring a bell?) So - where do we draw the line about prosecution of wrongdoing? Is it OK to prosecute in the Department of Interior but not in the Department of Justice. Or OK in the Department of Justice but not in the Department of Defense?