Sorry but the law isn’t going to see it that way even in Texas.
Self defense is to defend yourself.
Once the threat is neutralized, you don’t get to the walk up and put a bullet in their head.
Summary execution is not self defense.
He’s going to face charges.
Did you read the pot of the Deputy Sheriff who no one is looking for the shooter? No one cares, and no one thinks the guy would get convicted to begin with.
If the shooter is a gang member or an illegal, he won’t spend a day in jail. Houston’s DA is a hug-a-thug type. She turned out a cop killer like handing out candy.