There was a really interesting This American Life about this very subject. It does a great job of explaining some of the issues surrounding what Goldman Sachs did, though not about Goldman Sachs in particular.It does mention how Magnetar was supposably attempting to influence CDO managers into taking on riskier investment in order to get the CDO's to fail in order to cash in.
http://www.thisamericanlife.org/radio-archives/episode/405/i...