We don't really "know", but, here's my speculation based on the facts...
BTW...
June 15th or 16th
*Caylee was setting up to have Amy babysit Caylee @ a new rental [a.k.a. house#1]. She used the 'mini-vacation' 6/10-6/14 to search for house#1.
* On 6/5, Casey sends a Facebook message to Amy all giddy about getting her moved in "by the end of next week" which would be Sat., 6/14.
*Casey's m.o. is to spend nights @ Tony's starting on 6/10 w/o Caylee. Caylee NEVER spent the night @ Tony's, which was different than her arrangement w/ past boyfriend Ricardo - they all 3 shared the same bed. Casey may have thought Caylee's presence would ruin her chances w/ Tony and she wanted to (was) keeping Caylee out of Tony's life @ night until things were set.
All IMHO, of course.