Supposedly the FBI was tipped off that Galleon founder Raj Rajaratnam was conducting a little illegal biz by some traders who were none too happy with Raj-Raj, on account of being fired. Also, he apparently used to brag about his income to the now defunct Trader Monthly, which should be reason enough to lock him up (kidding? But also serious.) From former TM reporter Teri Buhl:
Raj loved to show up to the office in marine-style camouflage. He also was never shy about calling us to boast his income for the TM Top 100 story. In 07 we had him making $200m. His big score was in Galleon International ($1.5bn) from equity bets off Indian and Malaysian companies- up 31% in 07.