The cat in this film was called "Morris" and was well-known from the famous "9-Lives" cat food television commercials. The feline was also even billed in the movie's credits. Moreover, Morris had just recently won a PATSY Award for (as the acronym goes) Performing Animal Television Star of the Year (special award, commercials) for the previous 1972 year. Morris the Cat also appeared in another film noir detective film around the same time as Shamus (1973), that being in the same 1973 year's adaptation of Raymond Chandler's The Long Goodbye (1973) directed by Robert Altman.
There is a shot in the movie where Burt Reynolds grabs a tree branch during a chase scene, it breaks and he falls to the ground. That was not planned. The branch broke accidentally during filming and the footage looked so good, they kept it in the film.
A sequel to this movie, A Matter of Wife... and Death (1976), was made for television around three years later, and first broadcast in 1976. The follow-up does not feature Burt Reynolds as Shamus McCoy where the role was played by Rod Taylor instead. It was once reported in the media that Reynolds intended to appear in the sequel to this movie, but this did not happen. Producer Robert Weitman produced both movies with actors Larry Block and Joe Santos appearing in both films.
Second film from an Ed McBain (Evan Hunter) novel in two years for actor Burt Reynolds who had starred in Fuzz (1972) the previous 1972 year. That movie was also based on an Ed McBain novel but in that instance Evan Hunter) penned the script for the picture as well but not for Shamus (1973).
The phonetic pronunciation of the film's Shamus (1973) title was explained in the July 1973 edition of Movie News (Australia) magazine. It read: "Pronounced to rhyme with 'famous', it's a corruption of the Irish name 'Seamus' (James) tagged on to the New York Police force in the early 1900's when it was mainly composed of first and second generation Irish immigrants. Or pronounced to rhyme with 'Thomas', it comes from the Yiddish word for the sexton of a synagogue, frequently stereotyped as the guardian or officious 'policeman' whose job it is to keep order in the temple".
Before she said yes to doing the movie and playing Alexis, actress Dyan Cannon flew to Chicago to see her potential leading man Burt Reynolds performing in a play and to meet him. The very next day when she flew back to Hollywood she signed onto the picture.
The military sequences were filmed at the headquarters of the New York Army National Guard (NYARNG) 42nd Infantry "Rainbow" Division 1st Squadron 101st Cavalry which was located at 321 Manor Road, Staten Island, New York.
The picture is a homage to Raymond Chandler's novel "The Big Sleep" which had been filmed about twenty-seven years earlier in 1946 (see: The Big Sleep (1946)). Shamus (1973) was actually made and released about just five years before The Big Sleep (1978) remake debuted in 1978.
The casting of Burt Reynolds in the lead title role was determined by director Buzz Kulik and producer Robert Weitman based on Reymolds' earlier films that pre-dated his then recent big box-office success from 1972's Deliverance (1972) and had been sought for this movie prior to the release of that hit movie.
Burt Reynolds said of working with his co-star Dyan Cannon in his autobiography "My Life" (1994): "As Dyan and I walked down Broadway one afternoon a guy stopped us and asked for a picture. A camera dangled around his neck. 'Well, okay,' I said. Grinning broadly, he put his arm around Dyan and handed me the camera."
The movie is loosely based on the "87th Precinct" novels by author Ed McBain. Although the "87th Precinct" series of novels by novelist Evan Hunter (writing as "Ed McBain") have sold millions of copies since the first one appeared in the late 1950s, and still sell well today, this is one of only a relative handful of theatrical films (not counting a few made-for-TV movies and a TV series in the 1960s) to have been made from them.