Perfect crime 完美犯罪
Perfect crime is a colloquial term used in law and fiction (especially crime fiction) to characterize crimes that are undetected, unattributed to a perpetrator, or else unsolved as a kind of technical achievement on the part of the perpetrator. In certain contexts, the concept of perfect crime is limited to just undetected crimes; if an event is ever identified as a crime, some investigators say it cannot be called "perfect".