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So the killer stalks the family for weeks and then somehow walks in, since ther was no evidence of a break, in on Christmas ?
Why? I am friendly with my next door neighbors. I can tell you about what time they leave for work during the week and about what time they each get home. I can even tell you that on Thursday nights, the husband goes to his dad's for standing dart game so the wife will be home alone. However, I cannot even give a good guess whether they will be home on Christmas
They could be home all day and have guests. Or they could be going to a friends house and coming home about 10:00 P.M. Or they could be traveling out of town for the entire holday and won't be home until 3 days after Christmas. Or they could come home from their friends house at 10:00 P.M. and have Aunt Gladys and Grandma with them, so their kids might be sleeping with them and giving their rooms to the guests.
In other words, Christmas Day is not a day that anyone follows normal patterns. So "Stalking" people makes no sense if the intent is to commit the crime on that day! You stalk someone to establish their pattern. No one follows them on Christmas!
Also, it is not the day to be out of touch and busy waiting in someone's house for whenever they do or do not come home, for when they do or do not have guests staying at the house, etc. because your own family and friends will notice your absence. See I might not remember if cousin Jim was at Grandma's the last time I had dinner there. But if Cousin Jim wasn't there on Christmas I'm going to remember. I'm going to remember if my brother isn't around on Christmas Day.
So why would you stalk someone for weeks to attack on Christmas when you have no idea what the family you are stalking is doing that day? and why would you plan your crime on a day that everyone you know well is going to notice you were not around?
The timing of this crime has always steered me away from the IDI theory. Not, by any stretch, is that the extent of the reasons I bleieve RDI. It i just another in a very long list of common sense reasons.