As we know the FBI has had Dominic Casey's phone since Dec 18th I think. They have his pings, photo's, conversations and other from that phone. If you read what is reported today about the Press Conference you will notice it states.
No Press Conference From Anthonys' Private Investigators. That mystery caller could be a big clue that connects Casey to the crime scene.
Brand new evidence could potentially tie Casey Anthony to her daughter's body.A mystery videotape of the crime scene, shot by one of the Anthonys' private investigators weeks before Caylee was found, reportedly shows their other private investigator on the phone. But who is he talking to?
http://www.wftv.com/news/18411813/detail.html
So, I assume the FBI found what they needed to tie this case to Casey and make it rock solid "IMO".
I sure hope you're right!