I think Casey might have drowned Caylee deliberately on the 16th, although I can't then understand the need for duct tape. I keep remembering a moment in Cindy Anthony's testimony where she said that she and Caylee were enjoying the pool the evening of June 15, and Casey came home and wanted to get in with them, but Cindy told her no - that Caylee had had enough and it was time to get her ready for bed. I thought at the time "uh oh, classic sibling rivalry incident". I also think the nanny story came to be because Casey resented being reduced to being Princess Caylee's Nanny which she desperately wanted not to be. If Cindy had a history of playing with Caylee and then handing her back to her mother Casey with an admonition that playtime was over and duty was calling, that's plenty of motive and could be the trigger.
Or Casey could just have decided that somebody owed her a pool dip, so she took one the next day, and then didn't bother to put up the ladder because she knew she was "eliminating the child" next so that particular caution was no longer needed.
