Perry is depicted as being substantially taller than Truman when in reality they were roughly the same height. This may have been done purposely to give Perry a more intimidating presence next to the frailness of Capote.
When both prisoners are brought in to be hanged, it is raining hard. Even though the distance traveled in the rain is short, there are no visible signs of the rain on their clothes or face.
In Chapter One TC says no passenger trains stop at Holcomb - only an occasional freight. Yet Truman and Harper Lee arrive at (and she departs from) Holcomb by train.
Truman Capote: When you're talking to them, they seem like perfectly nice boys. To be frank, I'm much more concerned for my safety around Norman Mailer.