Specifically violent crime. Poor areas had more violent crime. These areas got dumped with more lead pollution. The rise percentage wise correlates almost perfectly with lead levels, with poor (and now polluted) areas rising more than well off areas. And then the drop, where after lead was removed from petrol you get a significant drop, but still less of a drop in areas more lead soil contamination, such of those blocks next to a highway. We know the developmental effects on young brains from lead; it is why we banned it.