Moore had Berg get with AlQueda (or vice versa)...they did the "film in the orange jumpsuit" thing with Nick IN ON IT....and then the AlQueda Actually DID behead Nick so he would never turn on them and give out any info he had on them. I believe Berg knew a LOT of AlQueda...beginning with Moussoui in OKC.
Why else would Berg's father say "they killed their best friend" and he was talking about AlQueda!!
I think that could be it. It started out as some kind of sppof, at least as far as Berg knew, but then got deadly serious. NO WAY were they ever going to let him go. I think that they had some of the same problems trying to understand what team Berg was on as we are having. But they know how to take care of such uncertainties.