Best way to research it is to read all the shit that tries to prove it. But don't stop at the comps like Hillberg's "Destruction of the European Jew" nor Yitzhak Arad's "Belzec, Sobibor, Treblinka" read the works of the people they cite like Wiernik and Willenberg that are mentioned in the pic I posted.
You start to realize the holocaust isn't very sound.
Link to Nuremberg transcripts:
avalon.law.yale.edu