My suggestion would be too ad a new zone that will only effect criminals and police. Give all current gangs turf and if possible make them border each other. Together these turfs will cover the part of the city that will be called the high crime zone. In these parts the gangs can shoot on sight if they see any rival gang members on they’re turf. They might also do a drive-by or an attack in a rival gangs turf. For this to work properly gangs must reinforce strict color and clothing rules, but most do already use they're gang color. Normal rules of engagement apply to civilians, but not for cops. Cops can be shot on sight by gang members, making this zone a place of danger for cops. Forcing them to only go in sparingly and always with a partner. Let’s be honest if you are a cop, you never really feel on edge. By having these zones you create a place where for the first time criminals will have the upper hand. There is no holding the zones game-play or anything like that, these zones are only for roleplay. Cops not being able to police the zone efficiently will make criminals naturally go there.