It was a sight that many people in the nonproliferation community hoped they would never see. On Feb. 6, Abdul Qadeer Khan stepped out of his home in Islamabad — essentially a free man — after Pakistan's high court lifted restrictions against him.
The 73-year-old Khan is considered the father of Pakistan's nuclear weapons program and is hailed in the country as a national hero. He also headed up a vast black-market nuclear weapons network, selling technology to North Korea, Iran and Libya. Khan has been described as the worst nuclear proliferator of all time.
Leonard Spector, director of the James Martin Center for Nonproliferation Studies' office in D.C., says Khan was unique because he was a great networker, and he had access to the technology.
"He had not only knowledge and know-how about uranium enrichment centrifuges and nuclear weapon design, but he had access to physical objects," Spector says.
Khan was able to distribute actual centrifuges that had worked in Pakistan but were no longer in use, he says.
In 2004, after a long international investigation, Khan admitted to illicitly spreading nuclear technology. His network was broken up, and several key operatives in countries such as Switzerland and South Africa were arrested.
But questions have lingered about whether Khan's network was fully disrupted.
Spector says virtually all of the operatives who were arrested have since been released. And now, so too has Khan.
Khan's Knowledge, Access and Assets Still A Threat
It's possible that Khan — who is ill with cancer — will live a quiet, uneventful life. But David Albright, president of the Institute for Science and International Security, says Khan still represents a risk.
He might sell off assets, such as nuclear weapon designs or centrifuge designs that might be held by the Khan network and remain outside Pakistan, Albright says.
"If Khan is feeling vindictive or feeling there is more money to be made, then he could actually try to activate some of the old relationships," he says.
Albright says he doesn't think Khan would be in a position to restart a network anything like what he had, but he would be able to sell surplus inventory.
Albright says there are potential customers: countries such as Syria, Burma or Sudan; terrorist organizations; or individuals who want the weapons and have the money to pay for them. Albright says one major concern is not knowing what information Khan still possesses — in his head or elsewhere.
For example, three sets of nuclear weapons designs — two of them partial — were discovered on a computer in Switzerland in 2006. Albright says those designs link back to Khan.
Two of the designs are for relatively small warheads — just the type that could solve Iran's problems, Albright says.
U.S. Worries About Release, Lacks Leverage
The U.S. pushed the Pakistani government to reverse the high court's decision. Pakistani officials say there will be "complete vigilance" when it comes to Khan: His calls will be monitored, his travel curtailed and his guests vetted.
When asked if the State Department was satisfied with Pakistan's assurances, spokesman Robert Wood sounded less than fully confident.
"Certainly, we have to take them at their word. But of course, you know, we'll have to see ... how things play out with regard to these assurances," Wood says.
At the moment, the U.S. can put only so much pressure on Pakistan to hold Khan, says Clark Murdock, a nuclear strategy specialist and a senior adviser at the Center for Strategic and International Studies.
"Why would the U.S. be making a big deal about A.Q. Khan — whether he's under house arrest or not — when you consider we [have] a lot more problems with al-Qaida leaders, whether they're in sanctuaries in northern territories," Murdock says. That, he says, is something the U.S. really cares about.
Spector, of the James Martin Center for Nonproliferation Studies, says Khan and his former operatives will likely be under very tight surveillance by everyone. He says he is more worried about the signal Khan's release sends: that Pakistan doesn't take nuclear weapons smuggling seriously.
"To me, the more damaging outcome was the symbolism," says Spector, "the fact that Pakistan did not stand by a tough nonproliferation commitment."