A shock investigation of possible insider trading at Standard & Poor's has reportedly begun, with the country still reeling from the rating agency's historic downgrade of U.S. debt. Authorities want to know who had prior knowledge of the decision, which sparked a wild week of trading on Wall Street that saw breathtaking losses and rapid rises. The Securities and Exchange Commission, which has oversight of credit rating firms, has started asking preliminary questions, the Financial Times reported. However, the regulator is not aware of a leak from an S&P insider,