I think it's possible that he latched the door because he REALLY did not one anyone entering the house by chance for any reason. He locked up, planning to get home and stage the scene that evening. He could wait a while, call around, finish cleaning and staging and THEN start reporting his wife and kids missing. Her got gazumped and had to let the police in before he could get anything set up. JMO. Another question, if he is trying to get the life insurance on the children, is this a motive for saying SW killed them? Could he still collect, if she killed them and not him?