The actual standard for LE is that of a how reasonable LEO (not a citizen) would act, with the information he had at the time he made the decision, given his prior training, general orders, state law and specific agency regulation(s) that apply if any. Additionally, the same elements to justify lethal force by a citizen with respect to imminent death or grievous bodily harm to the LEO also apply. Prevention of grievous bodily harm (eg, permanent disfigurement or physical or mental impairment, etc), justify the use of lethal force, if needed to stop the threat. This is not just limited to the prevention of lethal injury.
A requirement that the suspect be armed, BTW, is not part of the justification for the use of lethal force by either LEOs or citizens involved in a SD situation.
Another distinction between the justification for the use of lethal force by LE, not a citizen, is the prevention of lethal or grievous harm to the public in general. This is the reason that an LEO is justified in engaging in a pursuit of a fleeing criminal, if he believes the criminal still poses a threat to others beyond the LEO himself. In this case, the failure of the subject to drop the knife when ordered and his ongoing flight from LEOs, could reasonable be argued to fall in this category.
I believe most of us on the Fire are philosophically of a strongly libertarian mindset in our advocacy of individual rights. However, let's not forget that the vast majority of LE OIS take place in the course of the commission of a felonious act - in this case, the reported prior threat with the knife constitutes the use of lethal force, or at the very least aggravated assumption by the violator against the neighborhood kids, so his shooting fits the general pattern. Pointing a firearm at a person or use of a knife as a threat if the other elements are presebnt, constitutes lethal force by the offending criminal.
Also, given about 900K LEOs in the US, assuming only 2% deploy lethal force, that adds up to about 18,000 OIS events annually. Nowhere near that many OIS deaths per year, so the argument that LE is out to "murder suspects" is worse than misguided and groundless. Perspective is important, moreso than raw emotion in judging the facts.
