I haven't read all of the posts yet but I wanted to share a couple of thoughts before I forget them, (short-term memory is starting to slip)!! I hope I'm not repeating something that I just haven't read yet.
If Darlie did this to her own children, I believe that something in her just snapped. I don't know if it implies that she was a timebomb, or a sadistic sociopath. Maybe she simply just went over the edge temporarily due to the post-partum depression. (I've lived through post-partum depression more than once, and for those skeptics out there, let me just tell you ... it is 100% real)! For that reason, I don't think that she could have, after realizing what she had done, casually walked over to her son and stabbed him again to finish him off while she was on the phone. In a violent rage, yes ... as an afterthought to save yourself, I don't see it ... not in this case at least. Seems completely too far-fetched to me.
Irish Mist, I think your post about the direction of the knife on the counter is so insightful. I'm not sure if too much weight can be placed on the direction the knife was facing, however. We don't know which hand she carried it in, whether she placed the knife or kind of dropped or tossed the knife as she rushed by, (which could have made it spin a bit as it landed), etc. You also mentioned that the story never changed about where she found the knife. I thought I read on other threads that she first said the knife was dropped on the kitchen floor, and at another time said that she saw the knife laying on the utility room floor? I could be mistaken but I could have sworn I saw this.
About the pulse, I don't think it's unlikely that Darin wouldn't feel a pulse even if he was still alive at that point. This is a small boy who has lost a lot of blood, and is barely clinging to life. His pressure was probably extremely low and I think that even a trained medical professional might have trouble finding his pulse under those circumstances, certainly his frantic father would.
I also don't know if I would remember details in a situation like that. To us we can't imagine how the two of them can't get their story together on what Darin was wearing when he came downstairs. But think about it ... how surreal must this all have seemed? Even if Darlie did this, imagine what this scene must have looked like, and what kind of thoughts must be flying through your mind when you realize what you've done. And you wish you hadn't, (or can't remember that you did), and you're trying to call 911, and your husband is doing CPR on your baby, and the other baby is crying, and then you realize that he is dying too, and so on and so on. I can completely see how details like what someone is wearing could be overlooked. I think that a situation like that would be so chaotic that I would find it amazing, (and suspicious as far as Darin is concerned), if they both remembered with exact detail all of the events of the night and what each other were wearing, etc. To remember those kinds of details in this kind of context, I would think that you'd have to be fairly cold or otherwise emotionally detached especially if it were your children involved. Either that or it hints of premeditation.
Finally, I also don't find it weird that Darin pulled on his pants and put on his glasses first, (if that's what he did). I think it's a fairly quick & automatic reaction, and he probably had the pants he was wearing earlier draped over a chair near the bed or even lying on the floor next to the bed. He may have been hopping into his pants as he ran down the hallway so as not to approach whatever situation was waiting completely naked. This part of the story also does not concern me at all. If I were naked, I would almost definitely also reach for something before running out of the room.
This is not to say that Darlie didn't do this. I find the 16 versions of her story very disturbing, the silly string at the gravesite, (not to mention his friends at a graveside birthday party!!!! What kind of parents do these kids have????) But I do think that we all, (myself included), tend to overanalyze things especially when it's a case like this one that we simply cannot comprehend.
