Tit for tat murders really add up, except when the perps go to jail. I'm pretty sure the percentage of closed cases has skyrocketed. That really puts a hole in your murder rate.
Or those likely to murder in the 22nd District have left the 22nd District. Makes sense to me. The murder rate in the 22nd fell off a cliff. That area is also gentrifying, amazingly rapidly in places. Coincidence? I don't think so.
So we have two forces at work. Better, more proactive policing, and population shifts. Since both seem to be ongoing, I don't expect the recemt decline in murders to be an aberration.