Well, HItler wasn't "in charge" of the camps, Auschwitz for example was controlled by Hoss. DId Hitler order jews to be exterminated? There is no evidence that any order was signed by him to do that, did he know that was happening, most likely. Should he be held responsible for the actions , absolutely. As, for eye witness accounts, I am talking about when you get information from someone that says " my great great grandfather was there and told his son, that told their son, that told my father what happened" <- this type of information is highly unreliable.