Brutal: Satsujin Kansatsukan No Kokuhaku is a Manga/Manhwa/Manhua in english language, Adult series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

The manga centers on homicide detective Hiroki Dan, the son of a former police superintendent general, and who seems to be on the fast track to career success. He maintains a hidden identity as a serial killer responsible for more than a hundred murders of people he deems beyond the reach of the law.