Calling it a "plot to rival 9/11," DHS Chief Michael Chertoff tells ABC details about the London planes plot, which he says "would have killed thousands." On liquid explosives, Chertoff tells ABC's Pierre Thomas:

"There's no question that they had given a lot of thought to how they might smuggle containers with liquid explosives onto airplanes," Chertoff said. "Without getting into things that are still classified, they obviously paid attention to the ways in which they thought they might be able to disguise these explosives as very innocent types of everyday articles."

An interesting comment by an anonymous official:

One official who briefed ABC News said explosives and security experts who examined the plot were "stunned at the extent that the suspects had gamed the system to exploit its weaknesses."

How many test flights the terror suspects took has yet to be revealed.