Khan, who admitted in 2004 that he had leaked nuclear secrets to Iran, North Korea and Libya, worked as an engineer in the Netherlands at Urenco, an uranium enrichment plant.

In 1975, Lubbers the then minister of economy, received information that Khan was stealing nuclear secrets about the enrichment of uranium. He was never indicted for his activities because the CIA had asked the Netherlands to let him go, Lubbers told VPRO radio.

"The American intelligence services preferred not to arrest the man but to let him go. They thought: 'give us all the information but do not hold that man. Let him go, we will follow him and get more information'," Lubbers said.

That same year Khan probably felt his cover was blown because he never returned from a holiday to Pakistan.

Finally the Dutch authorities did open an investigation in 1979 that led to Khan being sentenced in absentia in 1983 to four years in prison. His conviction was overturned on appeal because of procedural mistakes.

At that time there were still possibilities to continue with the proceedings against Khan but the authorities again backed off at the request of the CIA, according to Lubbers, who had by then become prime minister.

"We were in the middle of the Cold War, debating placement of medium range missiles here. At that time I thought the final word about (Khan's prosecution) was not in The Hague but in Washington," he said.

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