Failure to prosecute crime leads to crime stat drops.
Besides, GP is flat out wrong - not prosecuting crime does not result in reduced crime stats. The crime decline is led be a relatively huge 15% reduction in homicides. Even if those homicides remain unsolved or are not prosecuted, they still end up in crime stats. And unlike other crimes where you may argue they go unreported, when someone ends up dead (by usually violent means in a homicide) it rarely goes unnoticed.
Homicides are the one thing that are hard to fudge the numbers with, although I am sure there are a number of deaths reported where there is not a homicide charge and there could of been, that is not the point.
I've seen the result of a city deciding to report less crime, it works. The stats go down, people from out of town find the place more attractive, real estate goes up. They argue nothing reduces crime like cranes gentrifying.
There is much more to the cycle of crimes not reported and/or not being prosecuted. It definitely works to bring down the numbers and exponentially.
Of course the long term thing of cranes coming in and pushing out the poor may be the lasting change. Although I believe the criminal element adapts as well and chooses things based upon repercussions, so the amount of petty crimes can go up while the cranes stamp out the larger noticeable ones.
Which city?
Unless they're just ignored as "missing persons".