Gauging North Korea's nuclear power

A U.S. scientist who has seen the North Korean nuclear program up close warns against underestimating the dictatorship's capabilities

North Korea has been playing a game of show and tell with its nuclear weapons program for years in an effort to convince the West it is a bona fide nuclear power. Some of Dictator Kim Jong Un's displays are deceptive propaganda, but the American scientist to whom North Korea has been sharing its nuclear secrets tells David Martin the country should not be underestimated. Martin's report will be broadcast on 60 Minutes, Sunday, Jan. 14 at 7:00 p.m., ET/PT.

"We think if we apply enough pressure, we'll cause them to buckle. And my impression over the years is this is not a country that's going to buckle."

"I was immensely surprised by how much they showed me and with the openness with which they showed and explained that to me," says Sig Hecker, once the director of Los Alamos National Laboratory, where the U.S. nuclear arsenal began. Hecker has been to North Korea seven times and seen proof of its development of nuclear weapons. In 2004 the North Koreans handed him a sample of plutonium used in the manufacture of nuclear weapons and in 2010 he was taken inside a large building which contained 2,000 gas centrifuges used to enrich uranium to bomb-grade levels. What he saw and reported to American intelligence agencies changed their assessment of North Korea's capabilities. "It changed from one of 'we don't know exactly what they have, if they have enough to make anything' to the fact that they actually could have four to six bombs," he tells Martin.

Hecker is confident Kim will one day have a nuclear weapon capable of hitting the United States. "They're going to get there…that's one thing you can count on. We've tried to sanction them into submission. They've not submitted. They just keep testing and keep evolving," says Hecker.

Martin also speaks to David Albright, director of the Institute for Science and International Security who is one of the most knowledgeable scientists in the world when it comes to the North Korean nuclear threat. Robert Carlin, a former intelligence analyst for the CIA and the State Department has accompanied Hecker on a visit to North Korea. Now a consultant to CBS News, Carlin says he is impressed by the North Koreans strategy and resolve.

"There's nothing that appears that they don't want us to see. Very calculated," Carlin tells Martin. "I think they understand us better than we understand them... We think if we apply enough pressure, we'll cause them to buckle. And my impression over the years is this is not a country that's going to buckle."