Pakistan has reportedly freed Abdul Qadeer Khan from five years of house arrest. The former head of Pakistan's clandestine nuclear weapons program, Mr. Khan allegedly still heads a deadly international black-market network -- selling nuclear weapons technologies over the years to regimes in Iran, Iraq, Libya, Pakistan and North Korea.

Bizarrely, Pakistan's High Court freed Mr. Khan on appeal. His lawyer said: "The court has said as he was not involved in nuclear proliferation or criminal activity, there is no case against him. Therefore, he is a free citizen." Pakistan's Foreign Ministry said it is taking "all necessary measures to promote the goals of nonproliferation. The so-called A.Q.Khan affair is a closed chapter."

Mr. Khan is at the nexus of the world's illicit nuclear weapons programs and illegally obtaining the highly advanced bearings required for their centrifuges.

Obtaining centrifuges -- and centrifuge bearing technologies in particular -- were long considered the insurmountable obstacles faced by rogue countries with aspirations for nuclear weapons. Uranium hexaflouride gas centrifuges are incredibly complex and arguably the world's most advanced electromechanical devices.

As such, the components are extremely valuable on the world's black market. For example, Mr. Khan apparently traded gas centrifuge and bearing technology to North Korea in exchange for Pakistan gaining access to North Korea's entire long-range missile program.

In Iran, the nuclear program is now estimated to be running 4,000 to 6,000 gas centrifuges, based on the older P1 generation and using ultra-high-precision ball bearings. But their stated goal is to obtain the technology, skills and equipment to build high-efficiency P2 centrifuges with magnetic bearings and carbon fiber arms. Eventually, Iran said its weapons program will run a cascade of 54,000 centrifuges.

Mr. Khan's source for centrifuge and nuclear technology has largely been by theft from Urenco. Urenco is a British-Dutch-German consortium formed in 1970 to supply enriched uranium for European nuclear reactors. In particular, Urenco developed and used highly classified centrifuge systems and related technologies -- lately employing advanced magnetic bearing systems -- to separate fissionable uranium-235 from uranium-238. The separation is achieved by centrifuging the isotopes at 100,000 RPM and higher.

Urenco's page describing uranium hexaflouride enrichment for power generation
In the 1970's, A.Q.Khan worked for Urenco. In 1976, he suddenly returned to Pakistan. In 1983, Dutch authorities charged and convicted him, in absentia, of nuclear espionage for stealing details of Urenco's centrifuge and bearing technologies. Mr. Khan could not be extradited from Pakistan because by then he was a government official, appointed to head the nuclear program.

It takes a cascade of thousands of centrifuges, arrayed in parallel and in series, to produce uranium-235 in sufficient quantities for a weapons system. Fortunately, time itself is also a stumbling block; most of the world's nuclear experts agree it takes nearly 20 years to build the necessary infrastructure to support a weapons program, even if some of the advanced technology can be stolen or is supplied from the outside.