Shoot him through the wall and stop him from maybe hitting you, someone else in the house or some person walking out front when a shot goes out a window...or the guy next door in his bathroom shaving....
This scenario sums up what the average home owner is faced with, in regards to overpenetration. Without exaggeration I could more than likely kick my way out of my house through an outside wall, with a pair of heavy, steel toed work boots. There is nothing to stop me except drywall, insulation, chicken wire and stucco. Even my fat a$$ wil easily fit through a 16" stud spacing. Interior walls are even less of a obstacle. If my foot can go through it, so can a bullet. Most any bullet.
Once you drop the hammer you are responsible for that slug, regardless of the threat you are under at the time you let it fly. If you kill a child sleeping in their bed across the street,
"But the guy was SHOOTING at me!!" won't be much of a defense. Get out your checkbook because it isn't going to be pretty. If your a cop, much the same applies, except for the fact it will be the department that gets sued, most likely not the individual officer involved. Yes, he could lose his job, and may face criminal charges, but he'll be in better overall shape than you the citizen would be under the same circumstances.