From the incomparable Glenn Greenwald:
…If our political leaders can’t be held accountable for their war crimes and other serious felonies in foreign countries or international tribunals, and must never be held accountable in the U.S. either (because to do so is to “pour acid into our democratic machinery”), then it means that American political officials (in contrast to most other leaders) are completely and explicitly exempt from, placed above, the rule of law…
Go. Read the whole thing.
The fact that a person who committed an act which constitutes a crime under international law acted as Head of State or responsible Government official does not relieve him from responsibility under international law.