You're correct, there is no legal basis. In fact, the police have a supreme court ruling which affirms that the police has no legal duty or responsibility to protect anyone. Even when they're given roles that would imply the responsibility (such as serving in a school).

Could we hold police more accountable? Potentially. Will we? Based on historical evidence, no.

And without that accountability, this is just another deadly weapon, one they can and will (again, based on historical evidence) use with impunity.