It was rigged as an IED and exploded. Initial reports were that there were no casualties, but now it appears there are three.
Sarin has an antidote, but the damage it causes long term is considerable.
WHAT IS MOST IMPORTANT about this is that it marks an escalation in the war. The enemy combatants have used WMD on the US and its allies for the first time.
Abu Gharaib is yesterday's news now. The story is going to have to be, "WMD have been deployed against the coalition, how is the coalition going to respond to WMD in an urban warfare environment?"
There is no more moral high ground for the insurgence. We can bury prisoners a$$ up and park bicycles in them and nobody is going to have a problem with it.
The blast in North Korea isn't going away either. An entire town was annihilated last week, and everybody is wondering how it happened.