I think LE is just not showing their entire hand yet. Maybe they have information that has not been released.
I was thinking about how information comes out in cases where no body has been found. People talk, either because they feel personally blamed or threatened, or because they have confessed what they know to someone who spills the beans.
It's probably unlikely that Casey will decide to confess, although it would certainly bring closure for a lot of people if she did.
It is possibly that someone will be named as an accomplice and that person, in an effort to save themselves, may tell the story.
I've never seen it mentioned here, but I have thought this for a long time: remember Susan Smith, who drowned her 2 sons? She did that because her boyfriend did not want to marry her and inherit 2 children. He was going to break up with her. Maybe Casey thought that her relationship with Tony might be threatened by Caylee's presence. Plus, it appears that she's had lifelong control issues with her mother. Casey, like Susan Smith, might have thought that it would be better to be viewed as a grieving mother and get the guy she wanted, than to do the decent thing and walk away from a man who did not want your children.
Just a thought -