lead in gasoline caused lead poisoning, leading to an increase in violent crime. now most fuel is unleaded, reducing the incidence of lead poisoning, and leading directly to a decrease in violent crime
Yep. What's more, this effect is even seen in countries that had less lead poisoning to begin with, like Sweden. Average blood lead levels in Sweden were below the level that the US government even considered concerning at the time — but they still got a ~5% decrease in crime by phasing out leaded gasoline.
Lead makes people stupid & impulsive; and stupid & impulsive people do more crime.