An acquaintance of mine is a Holocaust denier, and we get into frequent arguments about it. Even after I showed him a big portion of the evidence there is, he chooses to ignore it and says that we can't be sure that those pieces of evidence weren't manipulated.
He also showed me some of his own pieces of evidence, and I researched those same pieces of evidence only to find out that they were deliberately manipulated (who would've thunk it?). After I did that, he said that he bases his arguments on "an analysis of the present world", saying that "corruption, pain, hunger, and anger" are all signs, somehow. When asked what he bases those arguments on, he did not reply.
So, what can I do? Is there even a chance? How can I prove hat the evidence we have is truthful and has not been manipulated?
I always refer to Samuel Fuller's footage, found most easily in the documentary Falkenau, the Impossible. Fuller was a director after his return from WWII, and made The Big Red One, an autobiographical piece from his liberation of Falkenau starring Mark Hamill. He shot color footage of his company's arrival and liberation and you can see the future director's style in those early shots. Because this is a primary source document I have witnessed it change minds of deniers and minimizers. I also recommend Errol Morris' Mr. Death, because it gives a detailed procedural explanation of how someone can get their facts wrong through the dangers of thinking you can apply the scientific method without understanding how to setup an experiment. It really lays out how you can maintain logic and make reasonable inferences but be led totally astray to a certifiably false conclusion by a single break in the logical chain.
You should take a look at our Monday Methods on Holocaust Denial. It has a number of resources that may be useful.
I am not a historian, but I do have some experience in debating conspiracy theorists, especially in the medical/scientific field (AIDS denialists, anti-vaxxers, etc).
In my opinion, the fundamental characteristic of a hardcore, "un-convince-able" conspiracy theorist is this: when you present evidence to prove their argument is wrong, they don't change their mind, they just change their argument. You can see this with the aforementioned AIDS/vaccination denialists: time and again their claims have been proven wrong, and they immediately just shrug it off and shift the goalposts to something else.
You also find that once you start debunking their claims, many of these people will take refuge in more vague, emotional, political type arguments, that cannot really be "proven" wrong the way a fact can. "AIDS is just a plot by white westerners to kill black people!", "Vaccination is injecting poison into helpless babies!".
The fact that your acquaintance has been presented with evidence that proves he is wrong, and has chosen to just ignore it and change his argument to something else, is not a good sign. The fact that he is also following the path of retreating into "it's just corruption and politics and blah blah blah" type rhetoric is an even worse one.
As somebody who is studying the Jewish expulsion of 1492, I would ask the holocaust denier if they know what the Jewish expulsion of 1492 even is, and whether or not it coincides with certain historical events. (I.e, in 1492, Columbus sailed the ocean blue). Then bring it back to current politics, and state that the entire reason holocaust denial is so problematic in the first place is because people who are uneducated in such things fail to acknowledge the holocaust happened. Then if the person gets confused again, just link them to the Sean spicer thing....