There's a saying that bad cases make bad law. This might end up being just such a case. Can an officer go to the backyard to look through windows on a well-check? Can an officer fire into a building at an unidentified person who has a weapon? Must an officer identify himself before issuing commands? If the officer is not in a legal position, can he still claim self-defense? If the officer is trespassing and can use self defense here, can the next criminal/killer validly make the same claim? God, this is a legal hornet's nest...
I believe the saying is "Hard cases make bad law"
This is only a hard case if we want to give police officers even more leeway in abridging the rights of the people. He had no right or cause to be in that backyard
acting like a prowler. At every opportunity, he and his partner did the wrong thing. At no point does any of their actions seem rational*- if they were planning to catch an intruder, the officer in the rear ought not be announcing his presence with a powerful flashlight. If they were planning on a "dynamic entry", why did they split up? If this were an actual welfare check, why didn't they knock on the door?
Further, the police officer made no effort to defuse the situation, just immediately started with the "Hands <BLAM BLAM BLAM BLAM> up!" (Only a slight exaggeration, given that less than a second passed before he started shooting after shouting orders
without even identifying himself at a window where he had no idea if he had been heard.)
This isn't a hard case. This is a stupid person who should never have been a police officer and he and the department will likely pay for it.
The officers' best defense is that they were bungling fools. And murdered a woman defending herself, her nephew, and her home because of it.
*While, from best reporting, the actions of the murdered woman seem completely rational and justified.