The boy known as Danny Burke in the movie was actually Bobby Rupp in Truman 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).
The film gives the impression that Capote and Alvin Dewey had a bitter falling-out about Capote's involvement in the Clutter case: "If those boys get off, I'm coming to Brooklyn to hunt you down!" In fact the two remained very much in touch after the publication of In Cold Blood: Dewey was a high-profile guest at the famous Black and White Ball that Capote threw to celebrate its success in 1966. Evidence that has surfaced after Capote's death about his looseness with facts in In Cold Blood shows him several times reworking events in Dewey's favor.
The director, Bennett Miller, and Philip Seymour Hoffman were both graduates of NYU's Tisch School of the Arts, in the Film program and Acting program, respectively, who collaborated together on projects during those years.