I have been saying that if the writing is markedly different then TKAM was definitely written by Capote. To make it appear more like Lee wrote it is why it was changed to first person narrative. Just a hunch.
People are upset about Atticus. The possible evidence that Harper didn’t write it makes me sick. But her and “Sissy Britches”, as she called Capote, were best friends who leaned on each other. I can see him handing her the story. Or taking her Watchman manuscript and pulling out the characters and making it another book as was supposedly suggested by the publisher at the time.
This is total conspiracy theory. They were best pals until her book hit the bestseller list and continued far longer than In Cold Blood. Then he never bothered with her again. It wasn’t like Capote to hid his light under a bushel - particularly if he was responsible for an American classic.
And people who are crying on tv about the “new” Atticus: he’s a fictional character, people!
Capote was gay. I’d bet Harper Lee is lesbian. Thus the having each other’s backs.