In the last scene, it can be seen how bad the Los Angeles smog was at that time. It sometimes was difficult to keep ones eyes open due to the intense stinging of the smog.
Marisa Pavan played a lone blind woman in this film. When she appeared in an episode of Alfred Hitchcock Presents (1955), entitled You Got to Have Luck (1956), she also played a blind woman left alone.
FBI Director J. Edgar Hoover objected to the script that was submitted to him under the working title of "Case File: FBI". He was not only concerned about showing details of criminal activity but also the countermeasures the FBI used and that information could be used by criminals in the future to avoid arrest. It appears the producers alleviated Hoover's worries, and the title was subsequently changed as well.
The producers struck a cross-promotional deal with the then popular clothing store, Ohrbach's. In exchange for having the Ruth Roman character be an employee of the store, Ohrbach's agreed to provide most of the female characters' costumes.
Most of the principal players drive 1954 model automobiles: FBI agent RIpley's is a 1954 Nash Ambassador Super, Dave Millison's is a '54 Lincoln Capri convertible, and Joe Walpo's is a '54 Cadillac sedan. Although not inappropriate to the time for the characters involved, this may also be a nod to keeping the film looking as "up-to-date" as possible in light of prolonged theatrical engagements and its inevitable release for television broadcast.