"The Enforcer" (1951) Humphrey Bogart

Under heavy police protection, gangster Joe Rico arrives late at night at the courthouse to testify against crime boss Albert Mendoza. There have already been several attempts on Rico's life but lead prosecutor Martin Ferguson reminds him that he himself faces plenty of charges unless he cooperates. After yet another attempt on his life, Rico gives his bodyguards the slip but falls to his death from the ledge outside the eighth floor window.

Without Rico’s evidence, Mendoza will walk away free. However, Ferguson believes that something else has come up in the investigation that might make the case, so he and police captain Nelson decide to go through the evidence again. Much of this is told in flashbacks.

The case began when small-time gangster James "Duke" Malloy burst into a police station and claimed to have killed his girlfriend under pressure from others. The police find only an empty grave and Malloy later commits suicide in his cell. Ferguson is brought in on the case and a check on Malloy’s associates leads the investigators to "Big Babe" Lazick. When Lazick refuses to talk, Ferguson threatens to jail his wife and put his son into foster care. Lazick then confesses that he is operating under the orders of Joe Rico, who gets requests to commit murders over the telephone. The killers carry out murders for profit, the idea being that they are hired at the request of someone else. The killer will have no motive for committing the crime and thus will not be suspected by the police, while the client with the motive will have a perfect alibi. Only Rico knows who the top boss is.

Lazick leads the police to the body of Nina Lombardo. It emerges that she was a contract whom Malloy was supposed to kill, but he instead fell in love with her. Though he tried to cover it up, Malloy’s associates caught up with them and forced him to kill her. Nina's roommate, Teresa Davis, tells the detectives that Nina's real name was Angela Vetto and that she was in hiding since her father's murder ten years before.

The police eventually find a mass grave filled with dozens of bodies. As the authorities close in on them, the gang begins to break up. Rico himself is hiding on a farm with his last remaining accomplices and witnesses their shooting by hired killers sent to silence everyone. Rico then contacts Ferguson, offering to testify against his secret boss, Mendoza. He reports that Tony Veto and his daughter Angela had witnessed Mendoza’s first murder along with her father but now there were no survivors for the prosecution.

Frustrated, Ferguson goes to Mendoza's cell and leaves behind the photos of his victims. He then returns to the evidence room and listens to a tape made of Rico's confession — which is not admissible in court. In it, Rico describes Vetto's daughter as having "big blue eyes"; Ferguson remembers that Nina Lombardo (assumed to be Angela Vetto) had brown eyes. On the other hand, her roommate, Teresa Davis, did have blue eyes and Ferguson concludes that Nina was fingered as Duke's contract by mistake.

However, upon viewing Nina's photograph, Mendoza reaches the same conclusion and, with the assistance of his attorney, dispatches two of his remaining henchmen to pursue the real Angela Vetto. Ferguson and Nelson arrive at Angela's residence, only to discover that she has ventured out for a shopping trip. The bustling streets make it challenging for them to locate her, prompting Ferguson to utilize a music store's sidewalk loudspeakers as a means to alert her of the imminent danger and instruct her to contact him at the store. Angela heeds the warning and promptly reaches out, prompting Ferguson to embark on a rendezvous with her, closely pursued by the relentless killers. In the ensuing confrontation, Ferguson manages to eliminate one of the gangsters while the other is apprehended. With Angela under his protection, he safely escorts her away, ensuring her ability to testify against Mendoza.