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Investigators seek alleged 20th hijacker

A global manhunt under way for Ramzi

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.

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.

The sources said he was supposed to be part of the team that hijacked the United Airlines jet that later crashed in rural Pennsylvania.

VIDEO CNN's Eileen O'Connor says investigators think Ramsi Binalshibh may be the missing man on the hijacked plane that crashed in Pennsylvania (November 15) Play video (QuickTime, Real or Windows Media)    CNN.COM SPECIAL REPORT  CNN NewsPass Video  Agencies reportedly got hijack tips in 1998  MORE STORIES Intelligence intercept led to Buffalo suspects Report cites warnings before 9/11  EXTRA INFORMATION Timeline: Who Knew What and When? Interactive: Terror Investigation Terror Warnings System Most wanted terrorists What looks suspicious? In-Depth: America Remembers In-Depth: Terror on Tape In-Depth: How prepared is your city?  RESOURCES On the Scene: Barbara Starr: Al Qaeda hunt expands? On the Scene: Peter Bergen: Getting al Qaeda to talk

Investigators are backing away from their earlier belief that a man arrested in Minnesota -- Zacarias Moussaoui -- may have been the intended 20th hijacker.

"We haven't anything to link him to September 11," said one government source, adding that authorities still believe Moussaoui may have been part of a possible future wave of attacks. Moussaoui is not cooperating in the investigation.

Moussaoui was arrested in August on a passport violation charge and was in custody at the time of the attacks. Authorities later found information about crop dusters and wind patterns on his computer hard drive, but nothing specifically related to any terrorist plot.

Moussaoui also raised suspicions because of his interest in attending flight school, but sources indicated that initial reports that he was not interested in learning how to land were wrong.