That doesn't justify or excuse crimes committed by police, regardless if it is 'policy'.
Sue them personally. 42 USC Chapter 21 subchapter 1983. Police have no 'immunity'.
Actually, all accusations of excessive force will result in a motion hearing to determine whether the officer is entitled to "qualified immunity."
The standard to determine whether an officer's actions were constitutional is known as "objective reasonableness." It is determined in accordance with the standard set by the U.S. Supreme Court in Graham v. Connor, (1989).
"[A]ll claims that law enforcement officers have used excessive force—deadly or not—in the course of an arrest, investigatory stop, or other "seizure" of a free citizen should be analyzed under the Fourth Amendment and its "reasonableness" standard, rather than under a "substantive due process" approach." …
A "seizure" triggering the Fourth Amendment's protections occurs only when government actors have, "by means of physical force or show of authority ... in some way restrained the liberty of a citizen," (Cits). …
Our Fourth Amendment jurisprudence has long recognized that the right to make an arrest or investigatory stop necessarily carries with it the right to use some degree of physical coercion or threat thereof to effect it. (Cit) Because
"[t]he test of reasonableness under the Fourth Amendment is not capable of precise definition or mechanical application," (Cit), however, its proper application requires careful attention to the facts and circumstances of each particular case, including the severity of the crime at issue, whether the suspect poses an immediate threat to the safety of the officers or others, and whether he is actively resisting arrest or attempting to evade arrest by flight. …
The "reasonableness" of a particular use of force must be judged from the perspective of a reasonable officer on the scene, rather than with the 20/20 vision of hindsight. See
Terry v. Ohio. The Fourth Amendment is not violated by an arrest based on probable cause, even though the wrong person is arrested,
(Cit), nor by the mistaken execution of a valid search warrant on the wrong premises, (Cit). With respect to a claim of excessive force, the same standard of reasonableness at the moment applies: "Not every push or shove, even if it may later seem unnecessary in the peace of a judge's chambers," (Cit), violates the Fourth Amendment.
The calculus of reasonableness must embody allowance for the fact that police officers are often forced to make split-second judgments—in circumstances that are tense, uncertain, and rapidly evolving—about the amount of force that is necessary in a particular situation. …
As in other Fourth Amendment contexts, however, the "reasonableness" inquiry in an excessive force case is an objective one:
the question is whether the officers' actions are "objectively reasonable" in light of the facts and circumstances confronting them, without regard to their underlying intent or motivation."
Graham v. Connor, 490 U.S. 386, 109 S.Ct. 1865 (1989)