Leakage of nuclear secrets out of Pakistan makes at least one thing clear, US experts say: Today it's more important than ever to plug such proliferation holes.
The steady drip of revelations about Pakistani scientists' activities also may call into question the nature of US relations with a country that is both an ally in the war on terror and a fount of Islamic fundamentalism.
Abdul Qadeer Khan, former head of Pakistan's nuclear program, has expressed sympathy with terror groups known to want nuclear weapons - as have some of Mr. Khan's key military supervisors.
President Bush may address these delicate questions as early as Wednesday. "It is necessary that Pakistan in general, and Khan in particular, provide every shred of information necessary to roll up this network outside of Pakistan," says Matthew Bunn, an expert on nuclear weapons at Harvard University's Kennedy School. "Locking down stockpiles of materials to make bombs is all the more critical if terrorists could have access to a bomb design."
Pakistan's reaction so far causes concern among experts. It's not at all clear, they say, that Pakistani President Pervez Musharraf will turn over information necessary to locate all the links in the chain. Nor is it clear that he will prosecute Pakistani scientists and military or intelligence officials who may have aided Khan's transfers.
The current relationship between Pakistan and the US is slightly curious, these sources say. To this point the US has been oddly restrained about the Pakistani revelations, for one thing.
"Waving the fear of an Islamic fundamentalist state isn't good enough," says David Albright, president of the Institute for Science and International Security. "We cannot risk an attack by a nuclear bomb."
Earlier this week, General Musharraf said the US made him aware of Khan's suspected proliferation activities three years ago, but didn't provide sufficient evidence until last October. That revelation follows Khan's confession that he alone was responsible for transferring technology to Libya, North Korea, and Iran, as well as Musharraf's pardon of Khan.
Still, many questions remain over who else in Pakistan may have been involved with the proliferation ring, and when the US discovered it. For example, in a speech defending the Central Intelligence Agency last Thursday, Director George Tenet said the CIA has known about Khan's activities for some time. In fact, he said he provided testimony to an open session of Congress in February 2003 about the threat posed by "private proliferators," euphemistically referring to Khan.
Mr. Tenet went on to say, "We discovered the extent of Khan's hidden network ... stretching from Pakistan to Europe to the Middle East to Asia.... Our spies penetrated the network through a series of daring operations over several years."
Those kinds of statements are what makes it hard for experts here to believe there won't be much more revealed about this underground network. And it raises the question: If the Bush administration knew about it earlier, why did it wait until October to confront Musharraf?
"Tenet is saying they knew more than what was publicly revealed," says Paul Kerr, a researcher at the Arms Control Association in Washington. "I would be willing to bet more will be revealed. [Khan] had a fairly clever clandestine network built up in this string of suppliers."
Others agree with that assessment about additional disclosures. In fact, many experts believe there had to be more complicity within the Pakistani government.
Those kinds of transfers, they say, could not have taken place without the aid of the powerful military - charged as protectors of Pakistan's nuclear program - and possibly its intelligence service.
These experts also worry about the possible transfer of plans and technology to terror groups. Khan, as well as his former military supervisors, has long been known to sympathize not only with other Muslim nations trying to obtain a nuclear weapon, but also with Islamic groups.
In a 1984 interview with the Pakistani newspaper Nawa-e-Waqt, for example, Khan accused the West of trying to dampen Pakistan's efforts to obtain a nuclear weapon. "All this is part of the crusades which the Christians and Jews had initiated against the Muslims 1,000 years ago," Khan said. He went on to say that the West was afraid that Pakistan might share its technology with Iraq, Libya, and Iran.
Moreover, the military general who oversaw Khan's work, Gen. Mirza Aslam Beg, has publicly sympathized with Al Qaeda leaders. After the US bombed Al Qaeda training camps in Afghanistan in 1998, General Beg spoke to reporters. "By the grace of God," he said, Osama bin Laden escaped the attacks. Beg has denied he knew of any nuclear technology or information transfers. But he also told The New York Times that the government "would not dare" to ask him about it.