However, it's just not a "Non-fiction novel".
It's a good novelization of a historical fact. Not a damn thing wrong with that. I also don't object to his creative recreation of conversations and events that he couldn't possibly have been at. Cornelius Ryan did that in "The Longest Day" and no one pillories him over that.
It's just that Truman fudged the facts when he had them available because it made for a better story and THEN bragged to George Plimpton and anyone else who'd listen to him that his novel was "immaculately factual".
Dear Truman . . . in a pig's eye.
Maybe it's the historian in me, but to have 8000 pages of notes (that he refused to ever show anyone since "the novel stands on its own"), and to still make blatant mistakes or even faking facts to make certain points just rubs me the wrong way. Paying Donald Cullivan to stand in for Capote in the jail scenes with Perry Smith is so unethical it's painful. It was wrong to try and pay Herbert Nye to not say anything about the book when Nye complained about how he and other Kansas Bureau of Investigation members were given short shrift by Capote. Now, there's nothing wrong with the fact that Capote and Albert Dewey became friends during the investigation. Dewey, according to everything I've researched was a good cop in his own right, but some of the stories attributed to him by Capote were actually other men on his staff.
And this just starts to scrape the surface of the errors, inaccuracies or blatant mistellings of the facts in the book.
As I said, it's a great novel, but its just barely more accurate than your average Wikipedia entry. There's a lot of story that Capote left out and let's just say, some people weren't quite as sympathetic as Capote made them out to be. It's probably a good thing people were a lot less litigious back in 1965 than they are today or Capote might have been passing out a lot of that $2,000,000 he made on the book to a bunch of people in Holcomb, Kansas.