Cops don't show up to serve a warrant with a tank of gasoline and a lighter.
I didn't say they did.
However, if one of theirs is dead, and 50+ bullets have hit the neighbor's house... goodness knows how many magazines this man has emptied at them, and they haven't been able to hit them.
They're not used to that level of bad guy. They're ineffective at stopping him. You're telling me they can't get their hands on something flammable and make it happen? Their own man is lying dead on the porch and they can't pull his body cause they get 30 rounds sent their way every time they get close.
Maybe after 5, or 10, or 15 minutes of seeing this guy endanger the entire neighborhood sending random rounds into houses, they make a quiet decision to just plain smoke 'em out. Not all that unreasonable - the dude is a public risk and he'll kill more, he's trying, and they can't stop him.