Күнәсыз қылмыс немесе шешілмейтін құпия

Colloquial term

A perfect crime is a crime that is undetected, unattributed to an identifiable perpetrator, or otherwise unsolved or unsolvable. The term is used colloquially in law and fiction (especially crime fiction) for both crimes committed as crimes foremost, and those committed as a kind of technical achievement on the part of the perpetrator. The term perfect crime connotes one that is (or appears likely to be) unable to be solved, which distinguishes it from one that has merely not yet been solved, or where everyday chance or procedural matters frustrate a conviction. In certain contexts, such as a poisoning, some argue the bar must be raised to where the mere detection of a crime having been committed renders it imperfect.

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. 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'. 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. By definition, it can never be known if such perfect crimes exist. Many "close calls" have been observed, however—enough to make investigators aware of the possibility of a perfect crime. Similar rationale contributed to the dissolution of Bullfrog County, Nevada, in 1989; because the county was unpopulated, and was not assigned to a judicial district, criminal trials could not legally be held there under Nevada state law.

In March 2009, a $6.8 million jewel theft in Germany was described as being close to a perfect crime, in that despite having DNA evidence (but no other evidence), the police were unable to bring the case to court since the DNA belonged to one of a pair of identical twins, and faced with denials by both, it could not be proven which of the two was the criminal. Other examples of one, or possibly both, identical twins avoiding punishment include juries unable to reach a verdict in a 2004 Boston rape trial, a 2005 Houston rape trial and a 2009 Malaysia drug smuggling trial.