I am going to put on my tinfoil tiara and say this, there may have been a connection between Berg and Moussaoui. Moore heard about it, possible through the elder Berg. Moore sought him out for the interview. The unthinkable happened and Nick Berg was murdered by those evil bastards.
I do not believe in coincedence. "All things happen for a reason", that is what I believe. The foundations of my belief go deep into my past and my religion. Nick Berg had an al Queda connection and the evil scum mudered him because they know no loyalty.