This is Fred Leuchter.
Fred Leuchter was the specialist in designing U.S. execution facilities who was called on, in the mid-eighties, by Ernst Zundel's defense team to examine the 'gas-chambers' at Auschwitz. Leuchter duly obliged and published his findings in the "Leuchter Report". Flawed but essentially truthful, its findings were later confirmed by Germar Rudolf and, I believe, by the Auschwitz Museum authorities themselves.
For revisionists, the day Leuchter's findings were presented to the Toronto court was the day the myth of the homicidal gas-chambers was finally laid to rest.