I agree with this, and your posts of last night to an extent, however I still think he may have accidentally killed one of them, hitting her too hard because of backtalk or hyperactivity, and then had to kill the other one. Sure, he was probably on pins and needles as to when Shan'nan would arrive, if he had killed them before hand. Maybe he was infuriated that there was any delay at all, and that provoked violence, purposeful or accidental, with the kids. If he had originally planned on having the whole time from 11 pm to 5:30 am to kill them all and get rid of them so it would look like she ran away.....I'd guess that he was just angry in general. And...combined with IMO some break up or ultimatum with the AP, all hell broke loose with him.