From the BBC:
Pakistani nuclear expert AQ Khan was not arrested when living in the Netherlands as the CIA was monitoring him, an ex-Dutch prime minister says.
Ruud Lubbers said the CIA had asked the Netherlands in 1975 not to prosecute Abdul Qadeer Khan, who is now dubbed the father of Pakistan's atom bomb.
I don't know why the CIA would stop Khan from being arrested in 1975, but it sure looks like a bad decision now:
Mr Khan admitted last year that he had leaked nuclear secrets to North Korea, Libya and Iran.