I have looked at this case from time to time and often wondered about Darin's involvement. I have flipped every scenario i could think of around in my mind and bounced off what i know of the evidence (not all the way through the transcripts yet) and only one scenario makes sense to me and appears to fit what i know of the evidence.
IMO Darin wasn't downstairs till Darlie wanted him to be. I think she was more then well aware of the acoustic limitations of her home and the fact Darin would be sound asleep till she wanted him to be awake.
What i think supports this is small and simple
-His state of dress: no shirt (to me this suggests he wasn't premeditating or participating in the murder of 2 of his 3 children, for that he would have surly got dressed, no?)
I know a big rebuttal to this is the fact Darin doesn't seem to have administered care to Damon. This isn't telling anything to me other then he has cpr/1st aid experience. One child was breathing and somewhat responsive, the other didn't even have a pulse. The logical way to organize yourself in order to maximize your chances of successfully preserving life would be to administer cpr to the child who needs it and first aid to the other. Since he has first aid/cpr experience it would make sense for him to automatically take on the more challenging job of cpr and delegate the easier job of first aid to Darlie. She wouldn't comply and going to get Karen was a desperate move in order to acquire the other set of hands he needed.
I don't think he was able to question her behavior immediately due to the situation. Although I think after the police arrived he did for a split second and that was what elicited her statement heard on the 911 call, something to the effect of 'someone came in here and intentionally did it'.
IMO Darin only allowed himself to look at her in that light for that split second and it was so horrifying to him he immediately jumped into denial mode. Denial so deep he can overlook everything to maintain it (his level of denial is comparative to Cindy A's IMO). After he made this internal decision, doing things to cover for her became possible.
This is the how his involvement makes sense to me thus far, my opinion only.
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The one thing i can never make enough sense of though is the damn sock. :banghead: What was she trying to accomplish