There are several projects aimed at compiling information about transgressions by police officers into databases, with varying degrees of public access. This page attempts to capture information about such databases.
Criminologist Philip Stinson Sr., J.D., Ph.D., a former police officer now at Bowling Green, tracks instances of police misconduct. Dr. Stinson is a professor of Criminal Justice at Bowling Green State University in Ohio.
The Henry A. Wallace Police Crime Public Database is a project of Stinson and his Police Integrity Research Group. The database provides summary information that is not otherwise aggregated or publicly available for approximately 12,000 criminal arrest cases of nonfederal sworn law enforcement officers (e.g., police officers, state troopers, deputy sheriffs) from the years 2005-2015. site 
Further discussion of & high quality references related to Stinson's database at wikipedia
USA Today Network's similar, queryable database
Numerous police chiefs whose past included significant misconduct. USA Today 2019
Several databases collected in this thread on Twitter