When Bernie Madoff, who engineered history’s biggest Ponzi scheme, was arrested, FBI Special Agent B.J. Kang was right at his side. Reuters reported that less than a year later, there was Kang again, in a “perp walk,” shuffling alongside a handcuffed Raj Rajaratnam, the former hedge fund star at Galleon accused of earning millions off illegally obtained stock tips. Now, agent Kang may be focusing in on Steven A. Cohen and his $12.9 billion SAC Capital Advisors, L.P. Reuters has learned that Kang investigated allegations of trading irregularities at SAC two years ago, though the inquiry concluded with no charges being filed against the firm. As a member of the Federal Bureau of Investigation’s securities task force, Kang is heading up the two-year-old insider trading inquiry that has collared Rajaratnam and led to criminal charges being filed against 19 others by federal prosecutors in Manhattan. It was Kang, too, who signed most of the court applications seeking permission to place wiretaps on phones used by Rajaratnam and several other defendants.