People across the nation were stunned by a particularly violent incident of police brutality in August 1997. Abner Louima, a Haitian immigrant, claimed he was beaten and sodomized with the handle of a toilet plunger by four New York City police officers, who then shoved the stick into his mouth, breaking several teeth. As with the videotaped beating of Rodney King by Los Angeles police officers six years earlier, Americans once more wondered how police officers could turn so brutally and so sadistically against the citizens they were charged with protecting.

Some officers and police experts blame police brutality on the “Blue Wall of Silence,” an unspoken law enforcement code of conduct that forbids police officers to speak out against a fellow officer. This code of silence, according to critics, leads many police officers to believe that their fellow officers...