Frontline: Now the whole question of the so-called centrifuge tubes, the aluminium tubes-- Nothing much has come of that, has it? And yet much was made of it.
Hans Blix: Oh, much was made of it. … We have learnt since then that the Department of Energy, which are the ones who do enrichment in the U.S., that they had also expressed doubts about it. I see that on the U.S. side of intelligence, they are still saying, "Well, there was one batch that was a little less precise, and there was another batch where the specifications were more demanding," etcetera. But to me, this looks more like a rear-guard action. They would rather end the whole thing by controversy than by an admission that it was wrong.
Frontline: So no one can say, "Well, there definitely weren't weapons."
Hans Blix: I think so. Controversy will be preferable to a judgment.
http://www.pbs.org/wgbh/pages/frontline/shows/wmd/interviews/blix.html