Missing is based upon the book The Execution of Charles Horman: An American Sacrifice written by Thomas Hauser (Harcourt, 1978). The controversial nature of the book was not lost in the move to the big screen. The accusations of the Horman family that the United States government had funded and assisted the military coup in Chile in 1973 and then permitted the killing of their son Charles by the new government were voiced loudly and backed by documentation obtained years after that fateful day. Some dialogue heard in the film is taken directly from dialogue that appears in the book.

Constantin Costa-Gavras in his making of the film remains rather true to the information contained in Hausers writing. The only criticism that may arise regarding this judgment is that the book places more emphasis on the presentation of facts. This is not to say that the movie was irresponsibly inaccurate, but that it is more incomplete in its citing of facts and events. However, because of the nature of films, it would be unrealistic to expect that what the audience views on the screen will follow exactly as it is written in the book. Costa-Gavras was perhaps forced to forgo the development of the complete history behind the case of Charles Horman in favor of unveiling the human drama apparent in the story, but what he chose to use in his film is adapted fairly accurately from Hausers book.