Leuchter collected a few wall samples, and claimed to test them for exposure to cyanide. He claimed that no traces of it were found. Leuchter gave evidence in the trial of Ernst Zündel, which did not prevent Zündel from being convicted under a Canadian "false news" law.
Leuchter's holocaust denial claims were refuted by mainstream scientists and historians. They note that the methods used by Leuchter to examine the gas chambers were fundametally flawed. They note that cyanide could penetrate the stone masonry of the gas chambers only to the depth of one-tenth of a human hair. Leuchter pulverized his brick samples and thus mixed the entire sample together, instead of only examining the surface of the bricks (where the cyanide traces may have been easier to find). More importantly, Leuchter did not examine the walls of the gas chambers until fifty years after they had been used; his critics note that it would have been virtually impossible to discover any cyanide at all using his method.
Leuchter is the subject of a 1999 documentary by Errol Morris, entitled Mr. Death: The Rise and Fall of Fred A. Leuchter, Jr. Supporters of Zündel and Leuchter claim that Fred was harassed by Jewish groups, lost his job and his family life was consequently ruined. Critics, however, state that Leuchter's testimony in the film was more damning to his own reputation, and Zündel's. Film critic Roger Ebert stated in his review of the film, "Anyone who leaves Mr. Death in agreement with Leuchter deserves to join him on the loony fringe."