Since these people were all captured during or as a result of armed hostilities against the United States, the Geneva Convention requires the convening of a military tribunal to determine if they are "Privileged (Lawful) Combatants" or "Unprivileged (Unlawful) Combatants" (see
Wikipedia - Combatant) If they are determined to be Lawful Combatants (which is doubtful given the definition) then they can be further tried in a formal military tribunal. If, as is more likely IMHO, they are adjudged to be Unlawful Combatants, then they are supposed to be tried in civilian courts.
Now I don't like it, but since, under everything I understand about the "Laws of War," these guys were all "Unlawful Combatants" and so should be tried as such in civilian courts. To try them in a military tribunal expands the concept of a Lawful Combatant to future terrorists and also warrants their safety if captured (a privilege not "guaranteed" to unlawful combatants since they are not legally protected by the conventions).
The only good thing about trying these guys in military tribunals is that the rules of evidence are less onerous and their appeals more limited. However, they will all be convicted regardless so why not do it in a civilian court where they are not afforded the honor of being considered "soldiers" rather than the scum criminals that they are.
Mike