Shot back-to-back with Infernal Affairs III (2003). While this is a prequel to Infernal Affairs (2002), the third instalment is a direct sequel to the first film.
The line that SP Wong says, "Evil prevails. Only the good die young," is a simplified translation of what he actually says in Cantonese which is an old Chinese saying.
In the scene where Ngai Wing-Hau's lawyer leaves the family claiming, "I'm not one of you" a copy of "Noble House", James Clavell's blockbuster novel about Hong Kong, can be seen on the bookshelf behind him.