I have no doubt about it.  What worries me is how many shipments didn't get through.  A kg of this stuff, back pumped through the plumbing in a high-density condo could inflict a lethal dose (LD) in almost anyone using water - drinking, bathing, cooking, maybe even residual drugs left over from the washing machine.  I'd bet a well-timed injection could kill 50% of a building with a few thousand people in it.    All it takes is about 200.00 in plumbing parts, a lease on an apartment (top floor), and a kg of fent/carfent.  Not a big barrier to entry.