I thought of the possibility of the tv being on as well, as there might have been background noise preventing them from hearing all the shots. I've also thought that maybe there was more than one, if the father had one of his own and confronted the intruder, there was a struggle, and when he took Jayme he also took the gun with him. It would have taken several minutes to get her out of the house, collect the gun and any other evidence he didn't want to leave behind. But for now we have so little to go on, I just don't know.