Perhaps I have my timeline all confused - but, sometimes I think it's because Fleet knew there was no body there earlier - and then, presto, it's there. He knew it wasn't there, because he checked that room. He knew something was afoot.
I still wonder that the R.'s thought they'd smuggle her body out. They still had planned to fly out to Atlanta. (and what the heck kind of parents do that when there child is supposedly abducted! :waitasec
I can't recall if they planned on leaving before or after her body was found. I do recall JR calling a lawyer pretty pronto. Forget the 'small foreign faction' - they were in it deep & they would have known just how, of course.
Anyway, I think FW put two & two together. But, why not just tell the truth - if he knew what really happened that night (which he might not have - he just knew there was no body at first).
Forgive me if I'm getting my timeline confused, etc. It's been awhile since I've pondered this all!
JR tried to arrange a flight to Atlanta right AFTER he found JB's body. Police heard him, and informed him he couldn't leave.