In November 1984, a Dutch court sentenced him in absentia to four years in prison for espionage. Khan had copied the plans of the centrifuge process and sent them back to Pakistan.

It is called a research center, but the Pakistan Institute of Nuclear Research looks more like a fortress. Layers of barbed wire surround the sprawling complex in the dusty hills at Kahuta, 20 miles southeast of Pakistan’s capital, Islamabad. Much of the facility is buried beneath the earth, a precaution…