Author of the original short story Ernest Hemingway liked the film. Prior to its release, producer Mark Hellinger sent publicity man Al Horwits to Sun Valley, Idaho, to give Hemingway a private screening. Hemingway had a pint of gin in one pocket of his overcoat and a pint of water in the other so that he could sip from them if the film got bad. After the screening, Hemingway held up the full bottles, grinned and said "Didn't need 'em".
This was Burt Lancaster's first movie role. He was the third choice for the part of The Swede, and was signed only after actors Wayne Morris and Sonny Tufts proved unavailable. Lancaster was an ex-circus acrobat from Union City, New Jersey. When producer Mark Hellinger saw the first rushes of Lancaster's performance in a private screening room, he was so pleased that he yelled "So help me, may all my actors be acrobats!"
The boxing match in the third flashback was filmed in a boxing arena for an audience of 2000 spectators. Burt Lancaster trained for two months with a boxing champion and played the part of the Swede with realism, against a real boxer, until his 2nd KD and TKO.
Former Warner Bros. producer Mark Hellinger, who had started his own independent production unit at Universal-International, initially wanted either Wayne Morris or Sonny Tufts to star in this, his first picture. Tufts was ultimately considered to be too inexperienced, and Warner Bros. wouldn't loan Morris, so Hellinger cast the unknown Burt Lancaster in his first movie. It made Lancaster a star.
After leaving Warner Brothers for Universal with The Killers (1946), producer Mark Hellinger initially wanted to borrow Warner director Don Siegel, but the loanout fee proved prohibitively high for a director of his limited reputation at that time, so Hellinger used Universal's Robert Siodmak. Ironically, almost 20 years later Siegel did go on to direct the remake, The Killers (1964).
None of the facts given in the astronomy lesson in the prison cell are accurate. The constellation of the Great Bear (Ursa Major) is nowhere near Orion, while the star Betelgeuse is improperly identified as the brightest star in the sky. However, Sirius, which is the brightest star in the sky, is close to Orion.
In-joke: In the scene towards the end of the film where Edmond O'Brien arranges to meet Ava Gardner outside a nightclub, O'Brien stands on the street in front of the club, waiting for Gardner to drive up. On the wall behind him is a poster, beginning with "Sir Arthur Hilton presents..." Arthur Hilton, an Englishman, was the film's editor.
The trivia item below may give away important plot points.
The first 20 minutes of the film, showing the arrival of the two contract killers, and the murder of "Swede" Andreson, is a close adaptation of Hemingway's short story. The rest of the film, showing Reardon's investigation of the murder, is wholly original.