[Hack&Lube]

They were in the preliminary stages of setting up for a dry-run. It was not an imminent attack whatsoever and I don't see any news reports indicating otherwise.

Liquid explosives can be anything from the classic TNT and nitroglycerin you see in Westerns (where they tiptoe around with a bottle of clear liquid to stop it from exploding from agitation) to stuff you can make in your kitchen sink from common household chemicals. Officials suspected explosives made out of stuff like acetone and peroxide like stuff you can get in cleaners, disinfectants, nail polish remover, etc.

The real threat is from the one individual guy that doesn't participate in cells, internet, meetings, etc. and so can't be infiltrated or detected. These guys were caught because it was a big group and operation and they always want to go out with a big bang and hit a dozen planes simultaneously.