From Photofocus:
Several freelancers as well as some credentialed photojournalists were jailed for days without charge or trial in the days immediately after September 11. New York Mayor at the time, Rudy Giuliani, seemed to declare war on photographers. He had the police block off more than a square mile surrounding the World Trade Center, calling it a crime scene. The Mayor ordered that anyone with a camera who even stopped or stood still near the area should be arrested and jailed.
Why did he do this? Was the former Mayor trying to get back at a press who was not always kind to him? Giuliani likes to think of himself as a serious photographer. Did he want to save the photo opportunities for himself?