In 2007, Orlando residents were furious to discover that an FBI informant had organized a neo-Nazi rally through one of the city’s mostly black neighborhoods a year earlier. “To come into a predominantly black community, which could have resulted in great harm to the black community? I would hate to be part of a game,” Orlando City Councilwoman Daisy Lynum said at the time, calling for a “full-scale investigation” into the matter. However, an FBI agent testified that his informant participated in the event, but didn’t organize it. The city’s uproar passed without a public investigation, full-scale or otherwise—until now....