The most important unexamined question is whether police are trained to use force immediately as a first resort before they assess a situation or determine if they are at the correct address. Are the police trained that the lives of police officers are so much more valuable than the lives of possible suspects, or a houseful of people into whose residence a heavily armed SWAT team enters, that police officers must not accept the risk of judicious behavior when encountering citizens? If this is the case as all evidence indicates that it is, then the police when they gratuitously murder members of the public are merely doing what they have been trained to do. As police are trained to use violence as a first resort, the police cannot be held accountable when they do.
Comment: Exactly. When police PR departments say their officers complied with standard procedures, they mean exactly that: standard procedure is to shoot to kill, at the drop of a hat.
Comment: See: Nationwide protests against police brutality in AmeriKKKa: Wilson gets away with murder, Anonymous: #HoodsOff "The war is on!" (and note the comments - there are actually people who agree with this paramoralistic justification for cold-blooded murder)