What plays in my head, MD, is Cindy's early statements about "I was giving them time to bond.." and things of that nature. There is something in that statement that my mind goes back too-like she feels guilty for letting Casey keep Caylee from her for that length of time (31 days), or those were the words she used when she last saw them...I am not being clear I know.
I know women like Casey with children...ok not exactly like Casey clearly, but I can envision a frustrated parent or parents saying look, it is time you grew up and took care of yourself and your child. Tough love, it is time to get out and find out what it is really like to parent and work etc....
But, because of something fundamentally wrong with Casey, instead of her crawling back to her parents with an "oh I am sorry, come rescue me" she killed her child and went on her way free as air.
George and Cindy might have actually started to believe that Casey was getting her life together and then as time went on and no Caylee anywhere, they had to start to wonder. jmo.