THIS IS TOTAL SPECULATION ON MY PART, NOT FACTUAL, and it's based on a compilation of information I observed today.
I think this could very well be the work of a man in the neighborhood who Jessica knew. He's probably a married homeowner. He planned this. He knew the mom slept all day. His wife left for work. He lured her inside, did what was done to her, and then very methodically dismembered her in the bathroom. That explains what NG speculates (about which she was adamant, and I believe her "source") that the body was (this is hard to type) cut into pieces and bagged, so it could be transported. The bag containing the midsection parts (left the most intact) is what they found yesterday. The rest may be scattered in various places.
He cleaned up the place in his house where he did this (e.g., bathroom, using lots of bleach) and is sitting back watching the media. He thinks he's smarter than LE. And that's why the FBI BAU said "hey, tell us about any unusual behavior". They're looking for real insider (i.e., family members, close contacts) observations. Except I think a wife would be in denial and never acknowledge her husband could do such a thing.
This reminds me of The Lovely Bones, which I saw again last weekend.