Research psychologist Sarnoff Mednick of the University of Southern California agrees that crime stays low if it doesn't pay. He compared the criminal histories of thousands of young criminals in Copenhagen and Philadelphia and found that consistent punishment was the key. Punishment delivered after every offense significantly reduced later offenses. But an offender punished for earlier crimes who received nothing for later offenses resumed criminal activity at higher rates. The big problem with our handling of criminals in America is that they're not punished.
People are usually surprised to hear that, because of all our prisons.
But it's true. The accumulation of evidence shows that crime is both deterred and prevented by the use of strict enforcement and meaningful punishment.