Helicopter Policing in L.A.

Depending on which Los Angeles neighborhood you live in, you might hear the buzz of a chopper overhead, seemingly all the time. In some places they’re called ghetto birds, which gives you an indication of where their presence is felt the most. For people on the ground, the choppers are more than a mere nuisance. How did L.A. come to rely on helicopters to police the city, and what are they doing up there anyway?