In some text message Casey wrote "my mother ows me" meaning that Cindy would babysit Caylee so Casey could go out. On the 16th when she had a movie and overnight date with Tony who didn`t want Caylee spending the night, she tried to call Cindy many times but she didn`t answer. Damn my mother ows me Casey might have thought.
I think the killing was done "on a whim" that night. Think about the consequences and lie your way out of it later.