http://cryptome.org/padilla-sum.htm According to al-Qaida (at least to my reading), THEY rejected the dirty bomb.
Padillia, again according to their own recently unsealed info (which may well be complete BS), was tasked to blow up apartment buildings via gas.
The whole dirty bomb thing is an DoJ Asscrack exaggeration, if you believe their quotes of their informers. Apparently Padillia brought up the dirty bomb idea, and even al-Qaida said it was a bad plan.
Asscrack seized on this to give his scary big-brother sermon from Red Square.
And, hey, whatever happened to the shoe-bomber? We're they pals or something? That level of terrorist sophistication (if there's anything to whole thing at all) is what we are dealing with here.