Fantastic piece looking at some tremendous work that suggest it was lead that led (no pun intended
) to the drastic crime rise leading up to the 70s and the reduction of lead that has led to the subsequent reduction since. Steven Levitt's abortion theory might take a blow after this given the strength in data across so many regions.
http://www.motherjones.com/environment/2013/01/lead-crime-link-gasoline
http://www.motherjones.com/environment/2013/01/lead-crime-link-gasoline