Perfect crimes are crimes that are undetected, unattributed to an identifiable perpetrator, or otherwise unsolved or unsolvable as a kind of technical achievement on the part of the perpetrator. The term is used colloquially in law and fiction (especially crime fiction). 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".[1]
A perfect crime should be distinguished from one that has merely not been solved yet or where everyday chance or procedural matters frustrate a conviction. There is an element that the crime is (or appears likely to be) unable to be solved.
As used by some criminologists and others who study criminal investigations (including mystery writers), a perfect crime goes unsolved not because of incompetence in the investigation, but because of the cleverness and skill of the criminal.[2] In other words, the defining factor is the primary causative influence of the criminal's ability to avoid investigation and reprisal, and not so much the ability of the investigating authority to perform its duties.
Would-be perfect crimes are a popular subject in crime fiction and movies. They include Perfect Crime (play), Rope, Double Indemnity, Special 26 , Strangers on a Train, The Postman Always Rings Twice, Witness for the Prosecution, and Dial M for Murder.
A murder committed by somebody who had never before met the victim, has no criminal record, steals nothing, and tells no one might be a perfect crime. According to criminologists and scientists, this casual definition of perfect crime exists. Another possibility is that a crime might be committed in an area of high public traffic, where DNA from a wide variety of people is present, making the sifting of evidence akin to 'finding a needle in a haystack'.[3]
An intentional killing in which the death is never identified as murder is an example of one of the more rigorous definitions of perfect crime.[1] Other criminologists narrow the range to only those crimes that are not detected at all.[4] By definition, it can never be known if such perfect crimes exist.[4][5] Many "close calls" have been observed, however—enough to make investigators aware of the possibility of a perfect crime.[4]