(at around 48 mins) During the "take" speech, Reles throws a liquor glass at the door behind him. The glass leaves a nick and the door opens a few inches. In the next shot, the door is nearly closed and there is no nick. In the next shot, it's open wider again and the nick is visible.
When Joey and Abe are being kept under wraps by the police in a hotel awaiting their trial, the camera shows the exterior window of Joey's room first (on the left) then pans right to show the exterior of Abe's room (to the right of Joey's). Shortly thereafter, when Turkus walks down the hall from Abe's room to Joey's room, it becomes apparent that the configuration is just the opposite. As the drama transpires, it's confirmed that Abe's room was indeed the one on the left.
When Reles is upset because Joey turns down the apartment offer, he throws his glass and damages a closed bedroom door. When the camera returns to him, the cut in the door is gone and the door is still closed. In the next shot, the cut is back and the door is slightly open.
When Reales first meets Lepke, Lepke is eating cookies with milk. Lepke breaks the first cookie into three pieces to be able to dunk into his milk. When the shot changes, Lepke dunks and then eats, the first cookie. However, instead of three pieces, it is now two halves.
When Detective Sergeant Tobin tells the police guard to get Reles some water, Reles is sitting up in bed with his back against the headboard of the bed. When the scene cuts to a different angle, Reles is laying down on the bed with his head on a pillow.
Reles tries to make a deal with Burton Turkus that would give him total immunity in return for his testimony, but Turkus refuses, agreeing in the end only to protect Reles and not charge him with first-degree murder. In fact, Reles received total immunity for any crime to which he confessed being involved in.
Joe and Eadie Collins and their story are fictional. The key witness against Lepke after Reles' death was fellow mobster Allie Tannenbaum.
The idea that a person participating in a crime cannot testify against another person involved is ridiculous.
After two years of hiding out, Lepke surrendered to J. Edgar Hoover in Manhattan using columnist Walter Winchell as an intermediary. Other mobsters, concerned that the hunt for Lepke was bringing too much heat on them, sent word that Hoover had agreed to a deal that would keep Lepke away from state prosecutors looking to charge him with murder. Lepke believed it, but in fact, there was no deal.
During the opening credits, when Abe Reles' first victim is shown lying on the stairs apparently dead after being shot, he is clearly breathing.
When the detectives are discussing Abe Reles' death, the shot cuts to Reles' body, where you can see his right eye move, which is something Peter Falk couldn't control, since it was his artificial eye.
When Joe is trying to convince Eadie to leave him, he says "you're still pretty enough and young..." and his next line is "you're still young enough and pretty..." It appears Stuart Whitman decided to correct himself by repeating the words in the right sequence.
Joe Rosen was gunned down 13 September 1936, but the hit man arrives at the crime scene in a 1939 Buick.
Several times throughout the movie, the filmmakers apparently forgot that the setting of the drama was the 1930's (and early 1940's). From haircuts and clothing styles to the 1950's era hoodlums that Simon Oakland's character tangles with Rose's place, there are countless mistakes which reveal when the film was shot (vs. when the drama was supposed to take place). Women's hairstyles and fashions are continuously and conspicuously 1960 throughout. Primary cars stay more or less within the era, with a few notable exceptions, but here are frequently more modern, post-WWII era cars in the background.