Since there were posts here regarding Casey being the "only one with a motive to kill Caylee" and RK not having any motive: Of course I don't know about RK's motive or lack of motive either way so I won't comment on his motive or lack of motive. But regarding Casey as far as "motive": I think Casey had the least motive possible for killing Caylee. Despite the media's image of Casey as someone who would kill her child, there's actually no evidence (that we've seen so far, at least) to support this, and almost 3 years worth of evidence to the contrary. Not only did Casey love Caylee, not only was Caylee her only accomplishment and source of self-esteem, not only did Casey love taking Caylee and showing her off everywhere she went and always had, but if people want to be cynical, Caylee was also Casey's only meal-ticket, whether through her own parents or potentially the paternal grandparents or even through Caylee's father or the state.
And as far as the supposed motive of killing Caylee to be free to party or to be with TL, I don't buy it, because Casey had been much more head over heels about Brandon S than TL for example, and didn't get rid of Caylee to try to be with him or any other guy. And she'd always partied, no need to get rid of Caylee. But if she had wanted to get rid of Caylee, I think her MO would be just leaving Caylee with GA or CA and not returning, just stringing them along, saying she'd be back soon. So easy. I don't think it's in Casey's MO to harm or kill Caylee, or that Casey would ever want to go to prison for the rest of her life.
As far as motive goes, sadly, child predators kill children every day with no "motive". Casey had had Caylee around a lot of new people shortly before Caylee's disappearance. Casey had come into contact with a lot of new people. No harm had ever come to Caylee before, now suddenly Caylee disappears and is later found murdered.
Now, could Casey have murdered Caylee due to the onset of delusions, delirium, or some radical personality change that had occurred during those weeks or some unknown reason? Obviously can't rule that out either. In fact in her statements and jailhouse conversations, LE interviews, etc, I do think she appears deluded and appears to have had a significant change in thinking and personality, she's completely "blank" about Caylee, says many weird and muddled/confused things (which will be found out to be untrue immediately, serves her no purpose, no kind of calculated lying), seems to be confusing the past with her current life, even says that one of her friends was "Juliet Lewis" (i.e. famous actress's name.) So I do think she has had some kind of mental deterioration. Not that it necessarily means she was the one who murdered Caylee. MOO But I don't see real evidence of "motive" IMO.