Most major holocaust revosionists have depended upon the investigations of Fred Leuchter at Auschwitz and the samples he gathered from there for testing to bolster their claim that gas chambers are a myth.
The documentary 'Mr.Death' as well as professional historians like Robert Jan Van Pelt have scrutinized and debunked Fred Leuchter.
'Mr. Death: The Rise and Fall of Fred Leuchter'
Leuchter found what he called insignificant traces of poison gas in samples of the Auschwitz gas chamber wall which he chiseled off and took back to the U.S. in the late 1980's. He then submitted them to a professional lab for testing, but he made a cardinal mistake. He should have tested for traces of the poison only on the paint or the surface of the gas chamber wall. Instead, Leuchter broke off huge chunks of the wall and submitted them to the lab without mentioning where it had come from. The lab technician, by his own testimony in court, ground up the entire chunks into dust, and it is this dust that was tested. The lab tester did not learn where it had come from until after he testified in court. He says that his grounding it into dust destroys its validity as a sample. There may have very well been significant traces of the poison gas on the wall surface even after all those decades of exposure to the elements, but he grounded whole chunks into dust not knowing the area which should be tested because Leuchter had kept him ignorant of pertinent details including where the sample had come from and what he was trying to prove. Amazingly, evidence of small trace amounts of poison gas yet came out in the results which Leuchter prejudicial lot dismissed as insignificant. So much for his objectivity and reliability.