By luck or by cunning, some criminals evade detection and justice for ever. Of all crimes, the most worrying is the crime that is never solved. The criminal goes free, unpunished, often unidentified. Justice is not done. The friends and relatives of the victim - crimes always have victims - are left without closure. Whoever committed the crime is free to commit another. Law enforcers are pilloried for unsolved crimes for all of these reasons. But...