SNIP Representative Jane Harman, a California Democrat on the House Homeland Security Committee, said Friday that the packages seized in Britain and Dubai contained PETN, the same chemical explosive contained in the bomb sewn into the underwear of the Nigerian man who tried to blow up an airliner over Detroit last Dec. 25. That plot, too, was hatched in Yemen, a country that is regarded as one of the most significant fronts in the battle with extremists. Ms. Harman, who was briefed by John S. Pistole, administrator of the Transportation Security Administration, said that both packages contained computer printer cartridges...