If I remember correctly (haven't read this article), there's some sort of offset between decrease in lead and crime reduction, which seems to suggest that it is

If I remember correctly (haven't read this article), there's some sort of offset between decrease in lead and crime reduction, which seems to suggest that it is infants and young children who are affected, or lead actually affects the development of some areas of the brain (the offset was explained by the fact that infants and children don't usually commit crimes, but they do once they get slightly older). So it is not lead itself, (or the presence of it in your organism) that makes you more likely to commit crimes, but having your brain development impaired by it while an infant that does. I don't have time to search for the article, but it came up with the last discussion on this topic here.