Background on Mohamed Atta, Ziad Jarrah, and Marwan al-Shehhi -- where they grew up, what is known about their families, and how their paths led them to Hamburg, Germany, where they formed the core of the terrorist cell behind the Sept. 11 attacks.

From their arrival in Hamburg, Germany, in the 1990s through their final hours counting down to the terror attacks, this timeline traces the movements of Mohamed Atta, Ziad Jarrah, and Marwan al-Shehhi -- the men believed to have piloted three of the four hijacked planes on Sept. 11.

U.S. authorities found this letter handwritten in Arabic in the suitcase of Mohamed Atta. It includes Islamic prayers, instructions for a last night of life, and a practical checklist of reminders for the final operation. The FBI released an untranslated copy of the letter; the British newspaper The Observer published this translation. Additional copies of the letter were found at the crash site of United Airlines Flight 93 in Pennsylvania, and at a Dulles International Airport parking lot in a car registered to one of the hijackers on American Airlines Flight 77, which crashed into the Pentagon. [Note: According to The Observer web site, this translation was provided for The New York Times by Capital Communications Group, a Washington-based international consulting firm, and by Imad Musa, a translator for the firm.]

In October 2001, the German magazine Der Spiegel published a copy of Mohamed Atta's will, which was dated April 11, 1996. ABC News provided this English translation.