I think, other than being mentally disturbed, Casey is one smart cookie. I believe, unfortunately, that the worst has happened, that Casey did away with Cayley circumstances and manner yet unknown. She then decided to get rid of the body, a much easier proposition for a 2 year old than a full grown adult. It was either dumped in a lake, river, or dumpster somewhere. She then disappears for several weeks, hoping this much time will allow the body to decompose and be lost forever either to scavengers in the water, or in the bottom of a landfill. She then comes out of hiding and invents these ridiculous stories of where shes been and how Caylee was taken.
Her goal she doesnt want the body to be found, and in case she is still charged, she wants to go the insane angle on the defense. This is one cold-blooded cookie, I believe. I hope Im wrong, but I think this is another Susan Smith we have here.
I think if they can prove the dead body that must have been in the trunk was Cayley's, they should go ahead and charge her with murder.