MORE CRUCIAL of course than Fred Leuchter, the American consultant who hacked out the forty or so samples from the Auschwitz site and brought them back to the USA for testing, was the forensic chemist who conducted the tests. He was a Dr Philip Roth, employed by a highly reputable laboratory in New England. Roth, of Jewish origin, was not told that the test samples came from Auschwitz. He later spluttered (for the film Mr Death) that had he known, he would have come to quite a different conclusion. Quite.

Roth (and after him, Evans) also suggested that any cyanide stain would have penetrated only a few microns into the brickwork, making any tests on whole crushed samples meaningless. But photos showing revisionist scientist Germar Rudolf looking at the blue cyanide stain on the outside of a fumigation chamber at Auschwitz (right) show how improbable Roth's observation was: the blue stain has actually permeated right through the brickwork to the outside. Forensic tests on these stains showed them to have a very high cyanide content. But there was no significant cyanide content found on the walls of the Krema buildings alleged (until recently) to have been homicidal mass gassing chambers.