The closing arguments monologue was the longest in film history.
Although the story was obviously a thinly-disguised recreation of the Nathan Leopold and Richard Loeb murder case, the legal department of 20th Century Fox was still concerned about a possible lawsuit from the still-living Leopold. A great effort was made not to mention Leopold or Loeb in the movie, press releases, and interviews. However, there was apparently poor communication with the advertising department, since when the movie came out, newspaper ads stated, "Based on the famous Leopold and Loeb murder case." Leopold sued the filmmakers. He did not claim libel, slander or anything false or defamatory about the film. Instead, he claimed an invasion of privacy. The court rejected his claim in part because Leopold had already published his own autobiography "Life Plus 99 Years", publicizing essentially the same facts.
Because Orson Welles was having tax problems during the production, at the end of shooting his salary for the movie was garnisheed by the Los Angeles County Sheriff's Department. This upset Welles so much that just before he finished looping his dialogue in post-production, he stormed off the studio and left the country. All that was left to be looped was the last 20 seconds of his end speech in the courtroom. Incredibly, editor William Reynolds fixed this problem without needing Welles. Reynolds took words and pieces of words Welles had spoken earlier in the movie, and pieced them one by one into those 20 seconds.
The original play included what was then a modern-day sequence. This was omitted from the film. It showed several of the characters thirty years after the story took place.
Average Shot Length & Median Shot Length = ~11 seconds.
In his 1948 treatment of the Leopold-Loeb case, Hitchocock used his famous "ten minute takes" and segued from one to the other with a "natural wipe" generally focusing on the back of one of the character's suit jackets. Perhaps as a l'homage to The Master, "Compulsion" director Richard Fleischer uses a "natural wipe" focusing on the front of Bradford Dillman's suit to end a scene.
For some reason the appropriately gravelly voice of actor/wrestler Henry "Bomber" Kulky, playing the part of a speakeasy waiter, is dubbed by another actor.