The boy known as Danny Burke in the movie was actually Bobby Rupp in Capote's novel In Cold Blood, while the girl called Laura Kinney in the film is actually Susan Kidwell. The names were probably changed for legal reasons.
In the movie The Big Lebowski (1998), the photo that the PI shows the Dude of Bunny Lebowski's farm is the photo of the real Clutter home, where the murder chronicled in Truman Capote's "In Cold Blood" took place. Two "Lebowski" actors went on to appear in Capote (2005): Philip Seymour Hoffman (Brandt in "Lebowski"), plays Truman Capote, and Mark Pellegrino, (Blond Treehorn Thug in "Lebowski"), plays Dick Hickock (one of the murderers of that farm's inhabitants).
In the movie, Capote watches Perry Smith's hanging. In real life, Capote only watched Dick Hickcock's hanging. He couldn't stand to watch Smith die, so left before it happened.
A character in the movie pronounces it the "Arkansaw" River. According to a state law passed in 1881, this is the correct pronunciation, yet many people also pronounce it "Ar-kan-sas".
During the scene where Capote is drinking martinis with the Sheriff and his wife, they are using modern, "New York" martini glasses. The glasses at that time had a diameter of about 2 inches and stood about 5 inches high.