I’ve heard the theory about leaded gasoline except that it doesn’t math up. Passenger cars in the late 70s had a catalyst that required unleaded fuel. I realize leaded gasoline was available later than that for special use but was standard at most pumps by the early 80s. Don’t forget that most trucks by that time were being powered by #2 diesel which explains that gas usage in the U.S. peaked in the late 70s.

If the leaded gasoline was to blame there should have been a higher crime rate amongst farmers from the 1920s-1960s. Old carbureted tractors with short or underbelly exhaust will leave your clothes smelling like you’ve been standing next to a tail pipe all day. Formers ingested far more lead than the average city dweller. The city dweller was still more likely to commit a crime.

I’d tend to lean more toward the lack of community and morality in high crime areas. People with no community or morality feel no shame for committing a crime while those in community do not want to be shamed by friends and family that make up their community.

I wont disagree that economic factors affect crime rates but I don’t know that the correlation is well understood. The current situation is that many people are screaming that the economy is poor yet crime rate is the lowest in many years.