. >> robert carlin: they wanted to show sig that they really did have plutonium. >> martin: robert carlinnt his entire career studying north korea, first as an intelligence analyst at the c.i.a. and state department, now as a consultant to cbs news. here's a piece of plutonium, which in any government in the world would be one of the most tightly guarded secrets, and they hand it to an american? >> carlin: nobody would believe them otherwise, right? people would say, "oh, they're just posturing. oh, it's propaganda." so how are you going to convince the americans? you get an expert who knows plutonium when he sees it, and you, you hand it to him. you say, "here it is. what do you think?" >> martin: what impact did the information you came back with have on u.s. intelligence assessments of the north korean nuclear program? >> hecker: 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. >> martin: well, that's a fairly major change. >> hecker: that's a big change. >> martin: u.s. int