While the police code of ethics already requires officers to report the misconduct of others, it is not required by law. Officers should also be required to step in to prevent excessive force being used by another officer on any individual.
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This law should prevent complicity in the death or injury of individuals at the hands of other officers, and the use of excessive force in the first place. This would build on established restrictions already in place in the Criminal Law Act 1967 etc, and ensure greater accountability in such cases.
The individuals involved in these incidents are disproportionately of BME backgrounds and should be protected more significantly than is currently provided by the law.
Any use of excessive force or failure to stop and report it should involve significant criminal liability for the officers involved.