Don't be stupid 9/11 never happen its all an illusion. The buildings where abducted by aliens for creating a giant stone toilet back at there home world. ;) hope this post did not offended anyone.
it was obviously a pair of goa'uld death gliders cloaked as human planes and they were loaded with naquadah but good ol' SG1 managed to swipe the naquadah out of them before it was too late