“In this era of mass incarceration, the police shouldn’t be trusted any more than any other witness, perhaps less so. That may sound harsh, but numerous law enforcement officials have put the matter more bluntly. . . . Police departments have been rewarded in recent years for the sheer numbers of stops, searches and arrests. In the war on drugs, federal grant programs like the Edward Byrne Memorial Justice Assistance Grant Program have encouraged state and local law enforcement agencies to boost drug arrests in order to compete for millions of dollars in funding. Agencies receive cash rewards for arresting...