In 1991, the Christopher Commission was charged with investigating the causes of the riots that rocked the nation after the acquittal of the four Los Angeles police officers that beat black motorist Rodney King.

In a blistering report, it identified hundreds of officers who had been the targets of citizen complaints of excessive force, in nearly all cases against blacks and Latinos.

It took years and tremendous pressure from the Police Commission and the U.S. Justice Department to persuade the Los Angeles Police Department to drop its resistance to a computerized monitoring system that would better track civilian complaints regarding the use of excessive force.

Successive Minneapolis mayors, police chiefs, members of the police commission, and Hennepin County prosecutors, including for a time U.S. Sen. Amy Klobuchar, read the file on Chauvin, scrutinized the reports, examined the complaints, and investigated his trail of violence.

Again, police officials point to countless rules and regulations in their training manuals and policy statements about the use of deadly force.