I've been saying this for a long time, and think it is as true, or more true, than ever. The critical issue, though, is not so much the presence of absence of immunity for various actors so much as a national unwillingness to bring the guilty to justice. Only when a nation will not police its own does the international community have a right (and duty) to step in.
PS. Read the article by Philippe Sands, The Green Light, that Balkin links to.