Indeed. HDenier keeps repeating the same misunderstanding of how we know about the Holocaust - in fact, about any historical event or period (because the methods we use to investigate and interpret history do not change because of the object of study): it is not because of a single piece or kind of evidence that we can draw conclusions about the past but on account of a range of pieces of evidence of different types that when taken together create a picture of what happened.
In one sense what we have to explain is all that evidence: We have photographs of the camps, records of where many of the transports went (Gedob records and surviving Fahrplanordnung, bureaucratic correspondence) and other railway timetables, evacuation orders, inventories of goods stolen from victims, construction records (and Pressac's 39 criminal traces, e.g.), etc, various kinds of statistical records and reports, archaeological and other physical evidence at the camps themselves. Further, we have some interesting things like reports from killing squads themselves as well as from the Wehrmacht - some of these, the Ereignismeldungen, were used to convict Einsatzgruppen leaders of murder without witness testimony. We've got documents related to the use of gas vans (e.g., 501-PS and others). We have planning documents and discussion records; we have SS internal investigations and court decisions; we have military war diaries and diaries kept by Frank and Goebbels; we have decrees, orders, and other records relating to implementation of the Final Solution. We've got personnel records of the SS, other police organizations, and Wehrmacht, we've got official reports on the results of actions in making areas free of Jews. And so on.
And we have other documents - newspapers, records of parliamentary debates, speeches by political leaders, and committee hearings. We have diaries and letters written by victims and observers. we have a wide variety of photographs and newsreels and other film footage, we have forensic and medical information (physical studies use increasingly sophisticated investigatory and modeling techniques), we have geographic data and geographic modeling methodologies, we have census records, we have business documents, government decrees and ordinances, internal memoranda, meeting protocols, audio recordings, orders, telegrams, log books and ledgers, architectural blueprints, forensic reports and so on. Yes, we also have the one type of evidence HDenier goes on about, and misinterprets - memoirs, witness testimony, and oral histories.
Using all these kinds of evidence, scholars work out what happened, how, and what people experienced during the period. Unlike HDenier, they do not look at a single kind of evidence in isolation. Given the complexities of evaluating different kinds of evidence, much of it complex, and their interrelationships, historians debate how to best interpret it. Real revisionism is the use of evidence to come to new understandings - not mindless repetition of a few catch phrases or supposed debunking exercises. Real revisionists do not hop around from slogan to slogan but sort through previous interpretations and old and new evidence to re-evaluate historical topics. Also, it has to be noted that historians routinely, as part of their craft, subject all evidence to scrutiny to weigh its value and determine what it can tell them - HDenier's implication that scholars stupidly accept on its face values whatever they come across shows how little HDenier knows about how historians work.
