This is probably an off-the-wall thought, but I have wondered why the soldiers were described by the witness as "getting into a vehicle" with the masked attackers, which would imply that they weren't fighting back much. While it's possible that the witness is lying, I wonder if perhaps there was someone there they knew (an Iraqi) who gave them reason to believe that they would not be harmed. Then again, the details are so vague that I'm probably just letting my imagination get out of control. Still, I think relying on the Iraqis, while I know we have to do it for various reasons, could be a little risky for our guys.
It is a mystery to me also as to how they were captured. You may not be far off in your speculation.
And, if we still have the town secured, we should be able to find the killers.
Although we will never know all the details of this tragedy.