Apparetly the Jewish ORganization "Mossad" had warned several Israelis (not all) about going to work that day. And when the towers were falling many saw a Israeli film crew nearby cheering, this is why many thought Israelis were the ones who did this to tarnish the image of the arab world. Of course no proof of this but there was a documentary and it showed very good proof that the Israelis knew that the attacks were going to happen and I can't remember if they warned the US government or just warned their own people... it was in early 2003 when I saw this documentary