Read "The killing of Osama bin Laden" by Seymour M. Hersh. He is an investigative journalist and a regular contributor to The New Yorker magazine on military and security matters:
http://www.lrb.co.uk/v37/n10/seymour-m-hersh/the-killing-of-osama-bin-laden
http://www.lrb.co.uk/v37/n10/seymour-m-hersh/the-killing-of-osama-bin-laden