The key word is ‘rate’, as in per capita. The largest segment of society, the Boomer generation, has gotten too old to commit crimes on a level that keeps up with the population. Sure, we hear of more crimes now than twenty years ago, but only because we have more news outlets than we had before, and the old journalism adage still holds: If it bleeds, it leads. TV and print media still have to sell time or ad space, so what better way than to hype the horrible? ..................
When Memphis wants to make it look like crime rates are down, they annex a area that has very little crime.
Then you have the practice of Hierarchical Counting crime. If a woman is kidnapped, robbed, raped, and murdered, only the Murder shows up on the Stats. Rest flushed down the toilet.
The way things are classified makes a difference as well.
The Detroit crime rates are way down for the second year in a row but justified homicide is simply counted as a homicide with no distinction made between defense and murder. However even without the distinction being made the homicide rate is still down some 11% from last year. Where the real decline is seen is in property crimes like burglary and carjacking. Stealing a car or breaking into a building has become a much riskier proposition when the public is free to shoot.
The main drivers of the falling crime rate in Detroit are the fact that its an open carry / stand your ground city, they have a pro 2nd amendment police chief (GOP appointed), and an unemployment rate creeping slowly downward. (again due to GOP policies)