Crime and punishment.

Whether the penalty for theft is community service or death doesn't much matter if the odds of being caught are next to zero. Likewise, a relatively short prison sentence would be just as effective as the death penalty if one was assured of arrest.  

So when it comes to how to reduce crime, we should not focus on prevention as much as how to bring more cases to trial.  

While some criminals are just not bright, many simply discount the potential punishment by their probability of capture.  You can change their behavior by changing the answer to their expected value arithmetic, either by increasing the punishment or the probability of capture.

Legislating higher punishment is easy, but increasing the probability is more effective.