Middle Eastern men from a country beginning with the letter 'I' (Iraq? Iran?) set up video cameras aimed at the WTC Twin Towers before the first plane struck and were spotted celebrating after the impact.
http://www.foxnews.com/story/0,2933,34250,00.html
"The New York Times reported Thursday that a group of five men had set up video cameras aimed at the Twin Towers prior to the attack on Tuesday, and were seen congratulating one another afterwards."