When was it effectively phased out in Brazil, though? Leaded gasoline was mostly gone in the US by the 1970s and there was a 20 year lag before the crime rate started dropping. The wikipedia article says lead was banned in the US in 1995, but it was definitely not widely available.
However, if lead was widely used in Brazil right up until the ban date there (1989) then it would stand to reason that the crime rate wouldn't start dropping for another six or seven years.
I was buying leaded gas in Indiana as late as 1990, and had no trouble finding it in the general Illiana area. I don't think it's fair to say it was "mostly gone" in the 70s.
[By 1979 half of the gasoline in the US was unleaded](http://66.147.244.135/~enviror4/about/ethyl-leaded-gasoline/...). So by the early eighties it was mostly gone. So yeah, I slightly misspoke saying it was mostly gone in the 70s, but it was halfway gone by then.
However, if lead was widely used in Brazil right up until the ban date there (1989) then it would stand to reason that the crime rate wouldn't start dropping for another six or seven years.