His name is Kahn, he worked in the Netherlands, processing fuel.
They wanted to bust him for transcribing how to. But the CIA said wait, lets see where he takes the information.
He went back to Pakistan, when the CIA asked for his arrest and turn him over the Pakistani government said no to turning him over, and instead arrested him then pardoned him the next day.

The US wasn't too worried, they knew it would take a couple years to get enough fuel to try a bomb. But Kahn is smart, I mean really smart. They detonated their first bomb a mere 6 months later. He invented a new way to refine the fuel. Those same refining methods and units are in Iran now too. As Pakistan started selling the units to Iran. But got held up. So Iran started buying the materials from Russia, to finish them.

And now you know.