Factual error: Halfway into the film, a scene shows Capote talking on a beige telephone. The receiver is a modular (plug in) type. Modular phones were not introduced until after 1966. The time frame for this movie is 1959 through 1963. All other scenes in this movie show the correct type of receiver (wired, not plug-in).
Factual error: While Truman is in the supermarket the Campbell's soup can labels show UPC bar codes. The first codes were used on products starting in 1974.
Continuity mistake: When Truman is paying the warden for unlimited access to the two killers, he places a brown envelope with the money in it on the desk between them. In one shot he just places the envelope then draws back, but in another shot he places the envelope and pushes it forward before drawing back.
Continuity mistake: When Truman goes to see Perry's sister, Truman is sitting on a sofa in the living room, and behind the sofa is a large bank of windows. In the first shot there are 2 children playing in the backyard, but a second later, the children have moved - in fact only one can be seen at far left of the windows.