Of course. But this nuke story isn't that the terrorists set it off, it's that we found it in time, and took it out to sea where it wouldn't hurt us. So the terrorists wouldn't brag about that. But yes, so far, it's just a story. ;-)
Couple of thoughts:
(1)Nuke explosion offshore.
We know what the seismic signature of an underground nuke test looks like. The only thing on seismographs at about the right time looked like a normal earthquake.
What we don’t know is what a small nuke a little ways underwater looks like, nor what a small nuke in an open boat on the surface would look like on a seismograph. Nor do we have any way to detect a fizzle: triggering mechanism firing, but no nuclear chain reaction due to poor maintenance, old fissionables, misalignment caused by tech who couldn’t actually defuse the trigger to be certain there would be no blast, water getting into the mechanism accidentally, whatever.
So, short of Bush or Ashcroft coming out and admitting that this really did happen, it will remain a scary story to tell around campfires.
(2)Disruption of Cell communications.
However much I’d like to think that arresting the head honcho would leave the separate cells adrift, they probably have standing procedures for this eventuality, which involves checking a specific internet site for new orders.