Prof Schwarzschild Calculus:
A name like Muller is quite stereotypically German. Unless it is an assumed identity, I think it is safe to assume that he is German
Well, firstly, I have an Irish name, and it is "stereotypically" so (it's one of the most common Irish names, possibly the most common), but I am not Irish.
Secondly as I said, we know for a fact that Müller assumes identities; what we definitely
don't know is which - if any - of the ones we are presented with, is real.
It's therefore a big assumption to make that Müller is who he says he is, and too big an assumption to be taken at face value...
The examples of German you list are only found in the English, and as noted in the thread discussing his nationality, the French doesn't contain anything by way of a German "accent" to indicate that he anything other than a French speaker, so again, nothing definite there.
It's even possible that it's exactly what someone
pretending to be German would do, to corroborate their cover-story.
Prof Schwarzschild Calculus:
regards your statement about Nazi war criminals on the run being a staple for thriller writers , could you give a few examples
In addition to the books already mentioned, you could look for Orson Welles's 1946
The Stranger, in which he plays a Nazi living under an assumed name in a small town in Connecticut, while being hunted for his war crimes; it might be one of the earliest examples of the form, and is shocking for it's use of real concentration camp footage (not for exploitative reasons, it's sensitively handled in showing the mission of the Nazi hunters).
The 1956 film version of the story
The Most Dangerous Game, which was re-titled
Run For the Sun transfers the whole story to post-Second World War, and casts the villain as a Nazi officer, hiding out in the guise of a Dutchman (the irony being that the "Dutch" actor who played him, Peter Van Eyck, was in actuality a German - although the place he was born is now in Poland - who had left when he was twenty, toured around Europe and North Africa, before heading for the States where he wrote music for revues, worked for Irving Berlin and (coincidentally, Orson Welles), before changing his name, taking American citizenship, and joining the U.S. army to fight in the Second World War).
There are also things like 1961
The Twilight Zone episode "Death's-Head Revisited"; a little later,
Mission: Impossible had two stories about ex-Nazis being brought to justice in the first series alone.