One answer

It is recognised that criminal victimisation surveys provide the best measure of violent crime. When they have been conducted in NZ they show much higher levels of crime than either court statistics or police records. The latest criminal victimisation survey in the US shows violent crime has DROPPED from 49.4 to 20.9 per 100,000 people over the age of 12 between 1980 and 2005. Why? Because they are locking more people up.

Putting aside the futility of the 'war on drugs' and incarceration of drug offenders pushing up numbers, it is obvious that keeping dangerous criminals away from the public is one way to reduce violent crime. It doesn't need to be forever either. Most criminals burn out in middle age.