It's too bad that Khalid Sheik Mohammed confessed under the undemocratic conditions in Guantanamo. It makes the confession less believable and deniable by those who don't want to believe it, although it probably is true, at least part of it. The fact that he confessed to almost everything bad that's happened in the last 10 years are so, seems questionable, but he probably did at least some of them. The confessions to the ones he didn't do are probably due to torture, which makes you confess to almost anything whether you did it or not, or due to the fact that he wants to take the heat off of those who actually planned the other attacks.
In any case, the administration would have greatly aided its case in the court of world opinion by adhering to the rule of law in the treatment of its prisoners.