More on lead

short version
http://www.motherjones.com/kevin-drum/2013/01/lead-crime-connection

Followup, including George Monbiot being skeptical, then convinced:
http://www.motherjones.com/kevin-drum/2013/01/lead-and-crime-assessing-evidence
http://www.monbiot.com/2013/01/07/the-grime-behind-the-crime/

why leaded gasoline, or how corporations got what they already knew was a known neurotoxin into our gas supply (and it's still being made and sold to poor countries!)
http://www.motherjones.com/kevin-drum/2013/01/how-did-lead-get-our-gasoline-anyway
http://www.thenation.com/print/article/secret-history-lead

contains links to 20 page articles on international lead levels
http://www.motherjones.com/kevin-drum/2013/01/lead-and-crime-ill-be-melissa-harris-perry-show-sunday-10-am

lead paint and murder
http://www.motherjones.com/kevin-drum/2013/01/does-lead-paint-produce-more-crime-too

Personal observation: American white flight from the cities may have been motivated by a mix of justifiable fear of crime and less justifiable fear of black people, but in retrospect getting away from all the lead was sensible too. People are moving back now, to cities with lower crime rates (in fact, crime rates matching those of smaller cities) and lower lead levels to endanger one's children.