Although there is no comprehensive database on police violence, this project is one of the more comprehensive sources for data, including mapping projects, infographics, trends and analyses of police violence data.
The ARD reports include all deaths of individuals in custody (not just police violence). In 2014 the program was suspended "due to concerns over the program’s coverage and reliability." The program has undergone an assessment and study looking into the inconsistencies. Although it is still not a comprehensive gathering of police violence, the study looks at why the data is so unreliable.
Short article about the origins of policing, which came about as 'slave patrols,' or organizations directed to abduct enslaved people who had escaped the slave owners, as well as 'Indian Constables' and other groups directed to defend settlers against Native Americans. Written by Victor E. Kappeler, Ph.D.
A look at how police escalate and provoke peaceful demonstrations into becoming violent, despite a large body of evidence demonstrating that their actions lead to this. The Marshall Project, June 1, 2020.