Though most Americans dismiss if not deride international law, ironically the policing standards developed by the U.N., Council of Europe, and other international bodies affirm if not exceed our vaunted constitutional standards.
Many of the problems with American policing come down to the principle of reasonableness and the doctrine of qualified immunity, which the U.S. has adopted instead of the more common international standard of necessity and proportionality.
Reasonableness allows law enforcement officers to use lethal force when they believe it is “reasonable” to do so (based on their perception of the severity of the crime underway, the threat posed by the suspect, whether arrest is being resisted, etc.). Qualified immunity shields police from being sued except under the narrowest circumstances. In the already-rare chance that violence or death at the hands of police reaches court, the police officer’s assessment dominates, leading most often to “not guilty” verdicts.
The Supreme Court has nearly consistently given police a lot of leeway to use force; I recommend reading Sotomayor’s dissent in Mullenix v. Luna, where she argued that the Court is basically sanctioning a shoot first, think later” approach to policing. Having worked in both prosecution and defense, her perspective is uniquely more comprehensive than other justices.
However, under international law — which governs most other countries — the use of both lethal and “less-lethal” weapons (such as rubber bullets and tear gas) must be restricted to situations of necessity and in proportion to the associated risks. (Contrary to popular belief, rubber bullets and the like are not considered nonlethal; they are defined as “offering a substantially reduced risk of death when compared to conventional firearms”.) Foreign and international courts have found that the use of less-lethal weapons may amount to torture or ill-treatment if not “proportionate to the aim pursued, namely to disperse a non-peaceful gathering” and because the severity of the injuries are not consistent with “the strict use by the police officers of the force.” International law also lacks any equivalent to qualified immunity for police conduct.