The main problem, however, was an entrenched practice of credulous diplomacy, says Mr. Heinonen.

WSJ: The Weekend Interview with Olli Heinonen: How Iran Went Nuclear

But in any case, Mr. Heinonen notes, Iran's breakout would likely outpace the ability of the "international community" to respond.

WSJ: The Weekend Interview with Olli Heinonen: How Iran Went Nuclear

"We don't see it, " the IAEA's former top inspector, Olli Heinonen, said at Washington roundtable Monday on Iran's nuclear program.

WSJ: North Korea Nuclear Find Raises Fears It Will Share With Iran

Though he praises the professionalism of the IAEA's world-wide efforts on nuclear safety, Mr. Heinonen is mystified by parts of its record on Iran.

WSJ: The Weekend Interview with Olli Heinonen: How Iran Went Nuclear

Recently they seized plans for an entire nuclear programme in electronic form. 10.53.28 Aston OLLI HEINONEN IAEA Inspector A lot of this information is in computerised or electronic form.

BBC

"This was never mentioned in public, " says Mr. Heinonen, adding that as he rose through the agency he learned of other such nondisclosures by Vienna's supposed enforcers of transparency.

WSJ: The Weekend Interview with Olli Heinonen: How Iran Went Nuclear

Mr. Heinonen can't say as we sit in his office at Harvard's Kennedy School of Government, where he has been a senior fellow since retiring as IAEA deputy director-general in 2010.

WSJ: The Weekend Interview with Olli Heinonen: How Iran Went Nuclear

For now, Mr. Heinonen is most concerned about Pakistan.

WSJ: The Weekend Interview with Olli Heinonen: How Iran Went Nuclear

"Yes, it might, but not overnight, " Mr. Heinonen says.

WSJ: The Weekend Interview with Olli Heinonen: How Iran Went Nuclear