When we see the "prints" of the Richard Avedon photographs, the type of film can be seen in the black border - it reads as "Agfa APX 400". Agfa did not begin manufacturing their APX line of films until the 1990s. Moreover, Richard Avedon's preferred film for shooting portraiture at the time was Kodak Plus-X.
The light switch on wall was modern toggle-type "snap switch" with narrow profile handle and smooth plastic ivory colored cover plate with curved edges. I would have expected a wide profile handle (or perhaps even a push-button type switch) and a dark bakelite cover plate with the fine grooves, etchings and engravings common in houses of that era.
The rental car is a 1955 Chevrolet Bel Air sedan. In November of 1959, this car would be too old to still be in a rental fleet. The 1960 Pontiac sedan used by the state of Kansas certainly had an unrealistically long service life as well - into 1965.
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.
In a scene Capote complains that he has been on the In Cold Blood case for four years. In the next scene he is invited to a party celebrating the movie version of Harper Lee's To Kill a Mockingbird (1962). But four years after the murders would have been late 1963, and four years after he met the murderers in January 1960 would have been at least 1964.
In the arraignment scene for Hickock and Perry, the flag in the courtroom has 50 stars. In January 1960, the United States flag still had 49 stars. The 50th star for Hawaii was not added officially until July 4, 1960.
Harper and Truman are dining together in a restaurant. Shot from Truman's left, he is holding a glass in his right hand, and his left hand is empty. In the next shot, from his front, he has a fork in his left hand. A few seconds later, back to his left side, his left hand is empty again.
The car they use to drive around town keeps changing from a turquoise Chevy to an earlier model yellow and white Chevy. Sun shades on the windows are visible from inside the turquoise car, while the yellow car has none.
When the girl is knocking on the Clutter's front door we can see two large windows on either side of the door. In the inside shot, these windows do not exist, suggesting the inside was filmed in a different house.
When Capote's luggage is placed on the roof of the taxicab in Spain, it is clear that the position of the rope used to tie down the luggage changes between cuts. In some shots the rope tightly runs across the luggage. In other shots the rope is falling off the luggage. In addition, when the cab pulls away, the rope is not even there.
In the kitchen scene, when shot from Truman's back the martini glasses are empty, when shot from the hostess perspective the martini glasses are full. Truman fills the martini glasses at the end of the scene.
When Harper Lee is leaving Spain, Capote walks her out to the waiting taxi. When they both bend over to put her suitcase into the trunk, a cordless microphone unit can be seen just under Lee's shirt, attached to the waist of her pants.
When Nell and Capote are doing their research in Kansas, they are looking for a girl named Laura Kinney, who is portrayed as the one who found the Clutter family on that Sunday Morning. In the book, "In Cold Blood" Nancy Clutter's two friends, Nancy and Susan, are the ones that find the Clutter family dead.
According to William Shawn's sons, he did not arrange for Richard Avedon to take pictures of Smith and Hickock, did not arrange Capote's reading, and actually felt squeamish about the project. He also did not accompany Capote to Kansas for the executions.
Alvin Dewey learns of the arrests of Dick Hickock and Perry Smith as he is sitting down to Christmas dinner with his family and Capote. According to "In Cold Blood," he learned of the arrests on December 30, 1959.
Truman Capote never viewed the murdered members of the Clutter family at the funeral home, as he didn't arrive in Holcomb until several days after their funeral had taken place. According to "In Cold Blood", the detail about the heads of the deceased being wrapped in gauze was related to Capote by Nancy Clutter's friend, Susan Kidwell, who visited the funeral parlor with Nancy's boyfriend Bobby Rupp, while the caskets remained open.
Flipped shot: Upon entering the chapel of the funeral home in Holcomb, Kansas, Capote sees four closed caskets. Funeral custom and casket design dictate that the body be arranged so that when a casket is opened, the head of the deceased is always on the viewers left, and the foot-end of the casket is on the viewers right. In this scene, Capote approaches what customarily would be the foot-end of one of the closed caskets. Then he opens the lid and looks inside where we see the head and shoulders of the deceased.
The goof item below may give away important plot points.
The contents of the telegram from Perry Smith to Nell, just prior to the execution, are changed in Smith's voice-over. Smith's voice says it is addressed to Nell, but the telegram indicates it is to Capote; Smith says "you" twice, which in the telegram reads "him"; and Smith's voice-over omits "I understand" Capote's absence from the hanging, whereas the telegram specifies that note of forgiveness.