First, there's a plausible biological link between lead and violence. We can performed double-blind controlled experiments with mice and see it. Second, viole

First, there's a plausible biological link between lead and violence. We can performed double-blind controlled experiments with mice and see it. Second, violence decreased in a given state 15 years after that particular state banned leaded gasoline. And it decreased for the particular cohort that had grown up without leaded gasoline but not particularly otherwise. At a certain point you're left saying something like "Every time I point this gun at someone and pull the trigger they get struck by a bullet but this could be a spurious correlation!"