Read your state laws.
If a person is in fear of “great bodily harm” from an attacker they are justified in using deadly force to prevent that. Most state statues read such as this example:
“Great bodily harm” means bodily injury which creates a probability of death, or which causes significant serious permanent disfigurement, or which causes a significant permanent loss or impairment of the function of any bodily part or organ;
Great Bodily Harm”
“The term `great bodily harm’ as used in statute stating when an assault and battery becomes aggravated, is not susceptible of precise definition, but implies an injury of a graver and more serious character than ordinary battery. Herrington v. State, 352 P.2d 931, 933 (Okla. Cir.).”(15)
“Great bodily harm” means bodily injury which creates a substantial risk of death, or which causes serious permanent disfigurement, or which causes a permanent or protracted loss or impairment of the function of any bodily member or organ or other serious bodily injury.”(16)
It was up to the cops who arrested him to know their state laws on displaying/brandishing a weapon.