Hijackers Mohamed Atta and Abdulaziz Alomari board Flight 11. Atta's bags are not loaded onto the plane in time and will later be found by investigators. Investigators will discover airline uniforms in one of the bags. (Cullen and Ranalli 9/18/2001)
It will not be explained why Atta would have obtained these uniforms only to put them in his checked-in baggage, where he would be unable to access them.