OK, so how about a motive for this attack?
Look at the wider context here. On 9/11, we know for a fact that three airliners were hijacked by Islamist extremists. Two crashed into the World Trace Centre, watched by dozens of TV cameras. One crashed in a field, heard by several witnesses who were on the phone with passengers of that plane. A fourth airliner was also hijacked (unless anyone can explain what happened to Flight 77, which is still missing

) but because there is not the same weight of evidence surrounding it, there is room for the usual suspects to shout 'Government conspiracy!'. It is utterly ridiculous, especially on a day when we already know that three (count 'em) planes had already been hijacked with the intention of crashing them into high-status buildings.