Los Angeles, California: City of Angels, city of nothing. Ten million people living fast and breathing smog with no connections, no problems, no ties. A bustling city spread out from coastland to farmland to desert townships, from water to drought. The only chain that linked the desperate and disparate neighborhoods of this wide, sprawling town was the long, heavy arm of the Los Angeles Police Department, an unlikely, violent unifier for a dysfunctional city. Los Angeles was informally known as the “Gang Capital of the Nation,” and so it was no surprise that the authorities acted accordingly, earning a...