What if the reason they are cought in Europe and not in the US is because we require ID cards, residential justifications etc...while it 's much harder to track them in the US?
There are many other cases of alleged assassins in the US who are cought in Europe, put in jail and have not been extradited to the US (from practically all EU countries) because Death Penalty is applied in the US (it's not new).
If there are terrorists (with Ben Laden connections in Afghanistan) cought in Europe, it doesn't mean they have committed any crime in the US; they probably haven't even been in the US yet. Why would they need to be extradited in that's the case? Wouldn't it be more clever to keep them alive, so they can talk and reveal all the other things we don't know yet (like the terrorist networks, etc)?

Raoul