Maybe the husband did it
If the husband was reading (like he said), he had to hear the first shot (the little girl). The wife then had to go up a flight of stairs and then the husband heard several more shots. Was he reading the entire time? I am on my first floor right now. If I heard anything that sounded like a gun shot, my tushy would be up and running to see what happened. Sounds fishy to me. IMHO