While filming a scene in a subway tunnel, Inger Stevens and Rod Steiger were nearly asphyxiated by carbon monoxide fumes. Steiger said years later that when they were being given oxygen, Stevens tried to refuse it. She said at the time she wanted to die; Steiger and the crew had to convince her otherwise. Years later on April 30, 1970, when Ms. Stevens, who had a history of suicide attempts, was only 35 years old, she died of a drug overdose.
Although the movie is set in New York and uses some New York area locations some key scenes were filmed at Los Angeles. The entire sequence in which Joan Molner picks up the ransom money at a bank, works her way through the building across the street, and drives away in a car parked in the alley behind that building, is filmed in downtown Los Angeles, in and around the Farmers and Merchants Bank at 401 S. Main Street. In addition, the scenes at Steve's house (where Joan delivers the money) and the small market down the street where Paul goes to buy cigarettes were filmed in East Los Angeles.
The subway sequence near the end was shot at and in the old Hudson & Manhattan Railroad system (now better known as the PATH Trains), operating in Lower Manhattan, lower midtown, and New Jersey, which was in bankruptcy at the time. (Passengers had shrunk to 30 million a year, and one imagines the operators were happy for whatever access fees and publicity the production carried with it.) The station or stations used seem to be the Christopher Street station in the far west of Greenwich Village, and possibly the 9th Street station north and east of the former.
The film features two real TV newsmen. Chet Huntley was co-anchor of NBC's nightly news, titled the Huntley-Brinkley Report; Roy Neal was an NBC News correspondent.
The film was a mild success for MGM and showed a modest profit of $48,000 (equivalent to $518,444 in 2024) according to studio records. Two-thirds of the box office take was from outside the USA and Canada.