The Holocaust is often characterized as the greatest crime in the history of mankind. Yet for 44 years t a single forensic investigation into this alleged crime has ever been undertaken. This changed in 1988, when Fred A. Leuchter, at that time the only U.S. expert for execution techlogies, was asked by German-Canadian Ernst Zundel to go to Poland and investigate the facilities in the Auschwitz, Birkenau, and Majdanek camps which are claimed to have served as chemical slaughterhouses for hundreds of thousands of victims-also called gas chambers. Leuchter changed the course of history when he concluded in his report that the locations investigated could t have then been, or w be, utilized or seriously considered to function as execution gas chambers. Subsequently Fred Leuchter also went to other camps, where mass murder with poison gas is claimed to have happened (Dachau, Mauthausen, Hartheim). He then wrote a similarly devastating report which concluded that there were gas execution chambers at any of these locations. This study was accompanied by an antated bibliography about published claims regarding these three alleged locations of mass murder compiled by Dr. Faurisson. In a third expert report, Fred Leuchter described in detail the technique of execution gas chambers as used in the U.S. for capital punishment, and juxtaposed it with claims about alleged Third Reich gassings. In a fourth report, Leuchter criticized a book on gas chambers written by French scholar Jean-Claude Pressac. This edition republishes the text of all four reports and accompanies the first one, which has caused a huge controversy and triggered a landslide of new research, with critical tes and research updates, backing up those of Leuchter's claims that are correct, and correcting those that are t. Fourth, corrected and slightly expanded edition.