The explosive is peroxide-based.
The compound is colored red and sealed inside the false bottom of a sports drink bottle. The bottle has a false bottom so that the terrorists can swig a drink out of it with impunity.
The detonator is to be the flash of a disposable camera.
"Hey, Ahmed, I have watched many American thriller movies, and have a plan..."
Once again, I have the sense of living in a comic-book universe...
Update: it looks like it was probably methyl ethyl ketone peroxide, which is the (slightly) more stable variation on acetone peroxide, what the Evil Terrorists used on the London train bombings. I've read speculation that it was acetone peroxide, but that's a solid, not a liquid. And apparently makes nitroglycerine look stable. At least these guys are predictable: stick with what you know. Would have been interesting to see how far they got, though, as this stuff is also apparently sensitive to shock. Why even bother with a detonator? Just shake it up...
Oh, and just notice this: what was I saying about powders? How come no one was confiscating powders? Well, actually, would YOU want to be taking possession of something that was so unstable that very modest amounts of shock or friction could make it blow up? I didn't think so.