I don't believe in the IDI theory, but I take you up on step one:
1) On the Ramsey House thread, one of the members commented how dark the street was at night in front of the house.
2) I don't know how much we've argued that the killing and the ransom note took hours with the killer having full access to the 1st floor and the basement.
3) How would an intruder get out? That would be as simple as using the front door.
As for getting in, that could have happened while they were at the party or after they went to bed. John may have checked all the doors the family normally used, but this house had 6 doors on the first floor. He may have not checked an unlocked door. Entry may have been as easy as turning a doorknob. With everyone in and out of the house for the party, forensic evidence of the entry would have been next to impossible to find.
I can also see why John wouldn't admit to checking all the doors at night. "Oh by the way, I didn't check all the doors that night and so I'm probably inadvertently responsible for my daughter's death." Would you admit that to the police and the press? Could you admit that with your wife sitting next to you?
This case is already complicated enough and there are too many things that point to an "inside job". We don't need to validate John and Smit's theories about the basement window to show how the intruder may have entered/exited.
Of course, this is just my opinion.
I agree that an intruder could have gained entry through a locked door. But when cops arrived John told them he had checked all the doors and found them locked. He even went to the garage to check that one from the outside. So if an intruder left through a door he would have had to have had a key and locked it from the outside.
Although the basement window is a possible entry point, police would have found it locked as well. It was three months later that John would announce that he found it wide open and closed and latched it without telling anybody.
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