The bush administration has ignored the Geneva convention from the start of this "war on terra" and this is just one example. The geneva convention provides that any trials has to met the same due process standards as any military trial for the occupying force's own soldiers. The proceedings in gitmo that were just enjoined did not meet such standards.
Back in my freshman year of high school one of the cases being argued dealt with military justice and a good work on this topic was the book "Military Justice is to Justice what Military Music is to Music." Here the Bush administration was not even giving the detainees the same rights that a service man would get under the Uniform Code of Military Justice and therefore the proceedings were illegal.
What the US supreme court did in the gitmo case was to gut the Bush position that Gitmo is a legal no mans land where US courts had no jurisdiction. That position was based on a 1950 US Supreme Court decision that was stretched way too far. Now, the Federal Courts have jurisdiction over these cases and there will be some due process and basic rights.