According to the Wall Street Journal:
The case was a big victory for prosecutors. Much of the evidence against Mr. Gupta was circumstantial, including phone records that showed he promptly called Raj Rajaratnam after receiving confidential information. The billionaire founder of hedge fund Galleon Group then ordered his funds to trade on the inside information. Mr. Rajaratnam was convicted of insider trading last year and sentenced to more than 11 years in prison.
Mr. Gupta, who had wanted to testify in his own defense, ultimately took the advice of his lawyers and elected not to, believing his best chance at acquittal was to raise doubts about the government’s case, according to a friend of Mr. Gupta’s.