"Curveball" is the Iraqi exile whose lies were key to the Bush administrations case against Saddam on alleged WMDs, although US intelligence agents were not allowed to talk to him. He was an informant of the German Bundesnachrichtendienst. Thus many Americans criticized Germany later on, when they realized his stories about WMD were nonsense.
Michael Stickings writes that "Curveball" has now spoken publicly. Michael isn't impressed and concludes in The Moderate Voice:
The Bush Administration didn't get it so wrong because of Curveball, however much of a liar he may have been, but because it didn't seem to matter to the warmongers from Bush on down whether they got it right or wrong at all. There were ample warnings questioning Curveballs credibility, as well as the credibility of other such sources, but the warmongers believed what they wanted to believe, so rooted were they in their own fanaticism, and didn't let anything like the truth get in the way.
Still, I wish German and American intelligence agencies would cooperate more so that politicians cannot later blame the other country's agencies for misinformation, but that is probably too much to expect. Well, sometimes they work well together: German spy received US medal for support to combat operations in Iraq in 2003 and German Intelligence gave U.S. Iraqi defense plan.