In the name of protecting men and women in uniform, states across the country have made it nearly impossible to identify dangerous law enforcement officers with a track record of violence and other misdeeds. Records detailing their misconduct often are filed away, rarely seen by anyone outside of the department. Police unions and their political allies have worked to put special protections in place ensuring some records are shielded from public view, or even destroyed. A national tracking system for backgrounding officers is incomplete and not available to the public. More than two years ago, USA TODAY and its network of newsrooms across the nation set out to change that. More than two dozen reporters began collecting public records from the communities they covered and beyond. Also contributing substantially to the record-gathering was the Invisible Institute, a nonprofit journalism organization in Chicago that focuses on issues around policing tactics and criminal justice. We pieced together lists of decertified officers in more than 40 states. We collected logs and paper records related to 110,000 internal affairs investigations. We gathered information on 14,000 lawsuits against departments and fought to obtain so-called Brady lists, documenting officers flagged for lying and other misdeeds. Then we scoured story archives from our newsrooms and others to piece together the most comprehensive list of police misconduct cases ever built.