I think that there is more to it than that. When a government agent behaves in such a way where you believe that your civil rights have been violated the officer enjoys qualified immunity when there is no prior legal case in that jurisdiction with similar circumstances such that the officer would have reason to know that the act in question is a violation of civil rights. Yes it's rigged bullshit, but... If the policy of the department was to restrain a person in such a fashion in these circumstances that would be because they have not been successfully sued for this behavior. It seems clear that qualified immunity would apply, except that that would not serve the interest of the ruling class in this case. Those interests being the imposition of anarcho-tyrrany to direct white working class anger towards police and blacks while leaving the ruling class to continue their predations upon the nation.