“We can't breathe in business class. Somebody's got mace or something.”
“Nobody knows who stabbed who, and we can't even get up to business class right now 'cause nobody can breathe.”
- Betty Ong, Flight 11
Not necessarily explosive, but tactical chemical attacks have been a known capability for a while, and part of anti-terrorist training long before 2001. Something truly sophisticated from a superpower state would likely escape detection, (and therefore likely implicate such a state,) but the Tokyo Sarin attack by a cult in 1995 involved big bags of liquid.
(This isn’t a justification of any particular security search, just pointing out that liquid agents are not a non-existent threat.)
