Citadel Investment Groupgave the go-ahead to withdraw funds to its investors, who had previously been unable to take out funds under a ten-month ban. The firm also said that a banker it had hired to build an investment bank, Rohit D'Souza, was departing. The changes underscore the difficulties the firm faces as it struggles to diversify. It had halted redemptions in 2008, a particularly low year for hedge funds in general, and is trying to get back on its feet.