Guillaume Malle, a credit salesman at Goldman Sachs in New York, recently left the firm. Malle, who could not be reached, is not yet thought to have joined a competitor. At Goldman, he sold credit protection to insurance companies seeking to hedge their fixed income portfolios. Malle reported to Harvey Schwartz, a managing director in New York. He was traveling and could not be reached and Bruce Corwin, a spokesman, declined to comment.