Did anyone else catch...to me the most telling detail...when the cops were interviewing Casey after they revealed all her lies, and asking about the "phone" conversation with Caylee, how Casey said Caylee was not missing her, but would have missed Cindy, that she always missed Cindy?
The interviewer explored it a bit, but not in such depth but...to me...that jealousy, combined with what Cindy had said, was probably all the motive in the world.
Imagine this...what if Casey WAS trying/wanting to move out, and wanting to bring Caylee along (for whatever reason, to hurt her parents, whatever), and on their way out into the big wide world she was explaining to Caylee that they were going to live somewhere new and not with Grandma and Grandpa anymore. Then...Caylee gets upset. Very upset. Could that have triggered a rage in Casey, that Caylee wanted her grandparents more than her?