Public Enemy (2002) on Netflix

Plot summary

Kang Chul-joong is a tough cop who takes bribes and steals drugs from criminals, and with internal affairs investigating his conduct and his career in a slump, he is on a stakeout when he runs into a man in a raincoat in a dark alley and the two scuffle on the rainy street. The man slashes Chul-joong's face with a knife and disappears, and Chul-joong never gets a good look at him. A week later an old couple is found stabbed to death, and Chul-joong joins the investigation. He meets the couple's son, Jo Kyu-hwan, a successful business and family man, and then another killing follows the same pattern.