Kim Chan plays a crime-lord named Benny Wong nicknamed Uncle Benny. Chan also played a crime-lord, Ben Wong nicknamed Uncle Benny in Arma letale 4 (1998).
The film was originally cast with the Mark Walberg part played by Ethan Hawke, but production was ended to accomodate Chow Yun-Fat's production schedule.
In the original script, when Nick Chen walks in on May feeding Henry Lee grapes in the bath, she was supposed to be giving him oral sex. Chow Yun-Fat said that Chen would not continue a relationship with May after witnessing this, and the grape-feeding was suggested instead.
In the lamp store shootout and the massage parlor raid, there are close-ups of Chen shooting a criminal in the head at point blank range with a small revolver. These were directly inspired by Eddie Adams' famous Vietnam War photo of South Vietnamese general Nguyen Ngoc Loan executing handcuffed Viet Cong member Nguyen Van Lem on February 1, 1968.
Director James Foley decided that the movie should have a deliberately exaggerated visual style, with multi-colored fluorescent lighting, flashing strobe lights, and constantly moving handheld cameras with whip-pans and snap zooms, because he thought his last few movies had been visually boring and formulaic, and he wanted to "reinvent" himself as a filmmaker. He originally thought cinematographer Juan Ruiz Anchía would hate some of the ideas he had in mind, but Anchía loved them.