Malcolm Ritchie, senior equity index trader at Lehman Brothers in London, has returned to the firm after a year and a half on sabbatical. Ritchie, reached at Lehman, said he trades European indices, declining further comment on his sabbatical. Ritchie replaces Utz Oberhansberg, European index trader, who left the firm last month. Oberhansberg could not be reached and it could not be determined by press time if he will take a role at another firm. Vanessa Oakes, spokeswoman for Lehman, confirmed the replacement and said Ritchie reports to Mike Di Iorio, head of flow trading in London.