[Vince Ferrer]

The truth, Carnegie Mellon University criminologist Alfred Blumstein informed me, is that "no one has a definite explanation." Lots of factors may have played a role, and simple lessons are hard to find.

My guess is it mostly related to the baby boomer generation. When they were teens and twenty year olds, crime peaked, which is also the most likely age people commit violent crimes. They settled down and are now geriatrics, and so the crime rates fell naturally

[Niuhuru]

Quite right. But the boomers have imported plenty more criminals to make up for their feebleness and they are happily encouraging the production of more through illegitimacy.