The rates of violent crime, murder, and untreated mental illness directly correlate in the US with the rate of poverty. In locations where poverty is very high, the murder rate is very high (and that combo is amplified by population density).

That's due to the exceptionally mediocre social safety net in the US, among numerous other causes.

If you're in the bottom 1/3 you have very limited access to quality+sustained mental health treatment. If you're in the top 1/3, you have nearly unlimited access to getting treatment for a mental illness.

It's not millionaires roaming the streets of US cities looking like zombies, blasted out on drugs, hauling around untreated mental illnesses.