He had studied in Hamburg, Germany until June 2000, when he left for Florida to attend a flight school. His girlfriend in Bochum filed a missing person report. At his Bochum apartment, documents relating to airplanes and airlines were found.
On September 10, he sent a letter to his girlfriend, writing "I have done what I had to do" and "You should be very proud, it is an honor, and you will see the result, and everyone will be happy." as well as "Hold on to what you have until we meet each other again."
Because of an error in the address, the letter was returned to the U.S., where it was discovered.
His family in Lebanon claims that he was an innocent passenger on the plane or that possibly his is a case of mistaken identity and that he was not even on the plane. He has not been seen since the attacks.
See how he connected to the other hijackers: http://www.orgnet.com/hijackers.html
wikipedia.org dumped 2003-03-17 with terodump