It's not as critical knowing what's behind your target if you're shooting a shotgun AND you hit your target.
Besides, how do you know that Mr. Horn didn't take the precaution of knowing what was behind the scumbags?
No one got hurt, except for the scumbags who DESERVED it.
Good shooting.
Case closed.
No, he didn't check what was behind his targets, and at about 2PM you have gradeschool letting out.
Were young children in the area?