Television news is 100% worthless.
Looking at those pictures made me think of something. That person had a clear, perfect view of the brothers during the shootout. If he had a gun and shot them from his window, is that legal? Since he's not LEO and the gunmen aren't trying to shoot him, what's the law regarding that?
Generally, the doctrine of self-defense covers defending the life of a person if you reasonably believe that the person will be subjected to great bodily harm or death
andthe offender had no justification to use force against the person. In this context you'd be fine since you used deadly force to protect police officers, who were being subjected to great bodily harm or death, and the offender had no justification to use such force.
Those cases get a little dicey in the situation where the "offender," which the good samaritan shoots, was actually defending himself against the "victim." The law in most states places the good samaritan in the place of whomever they defend. So if that person would not have had justification, such as self-defense, to use deadly force, neither would the good samaritan.
TLDR; a person coming to the defense of another stands in the place of the person they are defending according to the law, in most states.
Here's West's most cited case on point in Massachusetts: "Actor is justified in using force against another to protect third person when reasonable person in actor's position would believe his intervention to be necessary for protection of third person and in circumstances as that reasonable person would believe them to be, third person would be justified in using such force to protect himself; ?reasonableness of such belief may depend in part on relationships among persons involved." Com. v. Martin (1976) 341 N.E.2d 885, 369 Mass.