On its face, the decision to release Mr. Abdul Qadeer Khan from house arrest in Pakistan is a slap in the face of international opinion and a blow to efforts to halt the proliferation of nuclear weapons. According to Pakistan’s Foreign Ministry, the work of the world’s greatest proliferator “is a closed chapter.” Were that the truth. Much remains unknown about the A.Q. Khan network and, without that knowledge, it will be impossible to ensure that the technology, materials and knowhow essential to the spread of nuclear weapons remain restricted.

Mr. Khan is a nuclear scientist and engineer, revered in Pakistan as the father of that nation’s nuclear bomb program. To help his country keep pace with India, its chief rival and neighbor, he developed a blueprint for a bomb — some say with Chinese help — and a network of suppliers around the globe to produce the components of a nuclear weapon. After Pakistan exploded a nuclear device in 1998, he was lionized for his work and given almost limitless freedom to expand his efforts. Convinced that the global nonproliferation regime was a form of nuclear apartheid, Mr. Khan was eager to serve customers around the world, and did business with governments in Libya, Iran, Syria and North Korea, among others.

Mr. Khan’s enterprises ended in 2003, when Libya decided to come clean about its nuclear ambitions — prodded by the seizure of a shipment of imported nuclear materials, which exposed its program — and Mr. Khan’s role in their realization. Pakistan arrested Mr. Khan, who then made a public apology for his actions, taking full responsibility. He was granted a pardon by then President Pervez Musharraf, put under house arrest and shielded from inquiry by other countries about his activities.

A decision this month by a Pakistani court ended the house arrest, which was in fact a step of questionable legality imposed by the Ministry of Defense. The new ruling puts Mr. Khan’s restrictions on a firmer legal basis and maintains restrictions on his activities, although the specifics of his “release” have not been confirmed. While Mr. Khan’s lawyer says he is now a “free man,” reportedly he cannot travel out of the country without advance approval — unlikely in any case given the risk of kidnapping — and has restrictions on phone calls, visitors and other activities. For his part, Mr. Khan says he wants to devote himself to education.

Apart from putting Mr. Khan’s restrictions on a solid foundation — rule of law is always to be promoted — the decision pays political dividends to the government of President Asif Ali Zardari. Mr. Zardari has been attacked for being too close to the United States, particularly with regard to policy toward Afghanistan and the Taliban. Freeing Mr. Khan is a nod to conservative and nationalist sentiment in Pakistan.

The decision creates a dilemma for the U.S. Mr. Zardari’s support is critical to tackling the growing insurgency in Afghanistan: The border provinces of Pakistan provide refuge for the Taliban as well as considerable material and logistic support. Yet the coalition forces’ offensive against the insurgents, especially the frequent attacks by drones on Pakistan territory, have alienated many Pakistanis and weakened Mr. Zardari.

At the same time, the questions that remain about Mr. Khan’s activities must be answered. It is still unclear who Mr. Khan did business with, how his network operated and what information he provided. For example, did he provide working bomb designs to clients? While it is very unlikely that Mr. Khan will again provide his considerable expertise to customers — both he and the Pakistan Foreign Ministry say his activities are a thing of the past — he could reactivate the network. Thus far, the Pakistan government has refused direct access to him, submitting questions from parties concerned to him and selectively reporting the answers. The U.S. must now decide how much pressure it will put on Pakistan for access and answers.

Islamabad’s reluctance to provide access to Mr. Khan reflects more than national pride. Mr. Khan at various times insisted that he was no rogue and that he operated with the approval, if not assistance, of his government. It is widely believed that the refusal to let others question him results from fears that others would be directly implicated as accomplices, if not partners, in his work.

That is only half the story, however. Western governments and intelligence agencies have been watching Mr. Khan for decades. While all the details of his network are not known, much is. His activities were tolerated for political reasons. The U.S. backed Pakistan on various issues and sometimes proliferation served geopolitical purposes. His activities also provided a window on the proliferation efforts of rogues. In other words, there is plenty of embarrassment to go around.

Despite all the questions that swirl around Mr. Khan, one thing is certain: He has forced the world to rethink its approach to nuclear proliferation. The conventional wisdom that such activities were the sole province of states and governments has been discarded. Determined individuals with money, creativity and patience can build a nuclear bomb. This is a threat for which the global nonproliferation regime was not prepared and represents the foremost security challenge today.

In a time of both misinformation and too much information, quality journalism is more crucial than ever.
By subscribing, you can help us get the story right.