At the time of the offense the offender is not worried that he might seize and punish. Excitement and doubt preceded unlawful act. Therefore, the crimes are carefully planned. The villain is convinced that his plan is perfect, and excludes the very tiny probability of getting caught. But professionals know CSI - any criminal act leaves a trace. Good searching, you can always find the evidence. And even when there is no evidence, is saving clue - itself a criminal intent, motive. Modern forensics and flawless logic in the service of law and order!