<p>WASHINGTON (CNN) --U.S. investigators believe that a man being sought by German authorities in connection with the September 11 terrorist attacks was the intended 20th hijacker, sources told CNN Thursday.</p>
<p>The man, Ramzi Binalshibh, also known as Ramzi Omar, is the focus of a worldwide manhunt. Sources said he tried to enter the United States several times with the help of Mohamed Atta -- a key figure among the alleged hijackers -- but never gained entry.</p>