I have actually heard this as well, but never checked. On the other hand I have heard that Chicago is crazy. Often the devil is in the detail (i.e. crime being confined to certain areas) when it comes to stats. It reminds me of the "Wire", the departments were changing the stats, not proof of course, but if they thought of it, I am sure that it has crossed the minds of others.

I think there was a youtube video of Thomas Sowell somewhere on this subject, I'll try and locate it.