The Taliban-Al Qaeda merger.

On July 25, Najibullah Zazi, a lanky man in his mid-twenties, walked into the Beauty Supply Warehouse in Aurora, Colorado, a suburb of Denver. The visit was captured on a store video camera. Wearing a baseball cap and pushing a shopping cart, Zazi appeared to be just another suburban guy.

Of course, not many suburban guys buy six bottles of Clairoxide hair bleach, as Zazi did on this shopping trip--or return a month later to buy a dozen bottles of "Ms. K Liquid," a peroxide-based product. Aware that these were hardly the typical purchases of a heavily bearded, dark-haired young man, Zazi--who was born in Afghanistan and spent part of his childhood in Pakistan before moving to the United States at the age of 14--kibitzed easily with the counter staff, joking that he had to buy such large quantities of hair products because he "had a lot of girlfriends."

In fact, the government believes that Zazi, a onetime coffee-cart operator on Wall Street and shuttle-van driver at the Denver airport, was planning what could have been the deadliest terrorist attack in the United States since September 11. Prior to his arrest last month, the FBI discovered pages of handwritten notes on his laptop detailing how to turn common, store-bought chemicals into bombs. If proven guilty, Zazi would be the first genuine Al Qaeda recruit discovered in the United States in the past few years.

The novel details of the case were sobering. Few Americans, after all, were expecting to be terrorized by an Al Qaeda agent wielding hair dye. But it was perhaps the least surprising fact about Zazi that was arguably the most consequential: where he is said to have trained.

In August 2008, prosecutors allege, Zazi traveled to Pakistan's tribal regions and studied explosives with Al Qaeda members. If that story sounds familiar, it should: Nearly every major jihadist plot against Western targets in the last two decades somehow leads back to Afghanistan or Pakistan. The first World Trade Center bombing in 1993 was masterminded by Ramzi Yousef, who had trained in an Al Qaeda camp on the Afghanistan-Pakistan border. Ahmed Ressam, who plotted to blow up LAX airport in 1999, was trained in Al Qaeda's Khaldan camp in Afghanistan. Key operatives in the suicide attacks on two U.S. embassies in Africa in 1998 and the USS Cole in 2000 trained in Afghanistan; so did all 19 September 11 hijackers. The leader of the 2002 Bali attack that killed more than 200 people, mostly Western tourists, was a veteran of the Afghan camps. The ringleader of the 2005 London subway bombing was trained by Al Qaeda in Pakistan. The British plotters who planned to blow up passenger planes leaving Heathrow in the summer of 2006 were taking direction from Pakistan; a July 25, 2006, e-mail from their Al Qaeda handler in that country, Rashid Rauf, urged them to "get a move on." If that attack had succeeded, as many as 1,500 would have died. The three men who, in 2007, were planning to attack Ramstein Air Base, a U.S. facility in Germany, had trained in Pakistan's tribal regions.