I don't think anything about what you just said can be assumed to be true. I am not convinced that increased police expenditure has a significant impact on violent crime, and even if it does I don't think it's reasonable at all to assume that violent crime rates would have increased without them.

I suspect that decreasing violent crime rates are caused by a constellation of forces (increased education, aging population, decreased alcohol consumption, more out there stuff like decreased childhood lead exposure, etc.).