Mad Detective is a Manga/Manhwa/Manhua in (English/Raw) language, Action series, english chapters have been translated and you can read them here. You are reading Mad Detective chapters on VipToon, fastest updating comic site. The Summary is
A mobster, who had no morals to speak of, was reincarnated in a parallel world as a detective in the Major Crimes Department by accident. With the help of a strange system, he solves cases time and again, eventually becoming a brash godly detective.