 That position was taken by the customer (John Paulson) who hired Goldman to issue the security (according to the SEC's complaint).Paulson and his employees selected 90 BBB-rated mortgage bonds that they believed were most likely to lose value and so the best bet to buy insurance for.Paulson and the manager of the CDO, ACA Management, worked on the portfolio of 90 bonds to be insured (ACA allegedly unaware of Paulson's short position), coming to an agreement in late February 2007.