Unanswered questions remain in September 11 probe

Zacarias Moussaoui is the only suspect to be charged in the U.S. in connection with the September 11 attacks.

From Susan Candiotti CNN Washington Bureau

WASHINGTON (CNN) -- They know who the hijackers were -- the 19 men who turned airliners into bombs at the World Trade Center and the Pentagon.

But six months later, the man overseeing the September 11 task force admits there are still holes in the case.

"We may never know everybody who participated," said Michael Chertoff, assistant attorney general in the U.S. Justice Department's criminal division. "But actually, I am encouraged by the fact that, as we have pulled together information that comes globally to us, we've filled in more and more pieces of the puzzle."

VIDEO CNN's Susan Candiotti reports, some involved in the World Trade Center and anthrax attacks may never be discovered (March 11) Play video (QuickTime, Real or Windows Media)    MORE STORIES  •  America remembers  •  The day the world changed  •  Unanswered questions remain  •  Hope in Kabul  •  Bush: World stirred to action  •  Giuliani looks back  EXTRA INFORMATION  •  In-Depth: September 11: A Memorial  •  In-Depth: War Against Terror  •  In-Depth: Day of Terror  •  People in the News: WTC survivors  •  TIME.com: Can we stop the next attack?  INTERACTIVES  •  3D animation: Tribute in Light  •  Gallery: Images of September 11  •  Gallery: Remembering 9/11  •  Quotes: 9/11 remembered  •  Lighting the Towers  •  Maps and Interactives Index

Investigators are convinced, for example, that the plan was hatched and developed mostly in western Europe and Malaysia, financed by Middle Eastern sources and executed by terrorists trained in Osama bin Laden's al Qaeda camps and at U.S. flight schools.

And it was carried out with remarkable secrecy.

"These are not people who are larger than life," Chertoff said. "They took advantage of the fact that something that was unthinkable on September 10 became, unfortunately, all too thinkable on September 11."

But in the last six months, only one suspect believed to have been linked to the attacks -- Zacarias Moussaoui, of France -- has been charged in the United States. Authorities still don't know for sure whether Moussaoui was meant to be the 20th hijacker.

In August, a flight school in Minnesota alerted the FBI that Moussaoui was so inept and intent on flying jumbo jets across the ocean that one instructor wondered whether he intended to use one as a bomb.

He was jailed on immigration charges a month before the attacks, but the FBI, despite suspicions, learned nothing more.

Focus shifts to Europe

Investigators say they linked Moussaoui and the hijackers to a money trail leading to the United Arab Emirates and on to Pakistan

They believe hijacking ringleader Mohamed Atta's former roommate in Hamburg, Germany, Ramzi bin al-Shibh, was a paymaster. He and others have been charged as co-conspirators on international warrants, but authorities don't know if they're dead or alive -- or whether other September 11 confederates are hiding in plain sight.

"Four thousand agents are still assigned to portions of the investigation, are still following leads to determine whether or not there are any associates, financial supporters or others who are still in the United States," FBI director Robert Mueller said.

While the FBI's September 11 case is not closed, sources say those U.S. leads have virtually dried up. The focus has shifted to Germany and other parts of western Europe.

The FBI's primary mission now is preventing another September 11.

"We're not so much focusing on making a criminal case as we are trying to understand what our national security risks are and then how we can harden American and our vital interests around the world from future hits," said Sen. Bob Graham, D-Florida, chairman of the Senate Intelligence Committee.

Using national security as justification, the attorney general rounded up more than 1,000 mostly Middle Eastern men last fall. Six months later, hundreds remain behind bars. The Justice Department won't reveal most of their names, and civil rights activists are suing.

"For a country that prides itself on due process and civil liberties, it's just indefensible," said Anthony Romero, executive director of the American Civil Liberties Union.

Anthrax mystery unsolved

After September 11, the United States also found itself vulnerable to biological warfare.

The anthrax letter attacks have stopped, but the FBI appears no closer to capturing the killer who claimed five lives and terrorized a nation.

"I will tell you we have no one person, specifically, that stands out at this juncture," Mueller said.

Letters containing the anthrax bacteria were mailed to several news organizations and two Democratic senators, Majority Leader Tom Daschle and Judiciary Committee Chairman Patrick Leahy.

The disease killed five people -- Robert Stevens, a photo editor for the Florida-based National Enquirer; two Washington-area postal workers, Thomas Morris Jr. and Joseph Curseen Jr.; Kathy Nguyen, a New York hospital worker; and Ottilie Lundgren, a 94-year-old Connecticut woman.

Another 18 people were diagnosed with either inhaled or skin anthrax, and dozens of people were treated with antibiotics after tests indicated they were exposed to the bacteria in October and November.