NEW YORK — Over the past half-decade, as federal authorities secured dozens of insider-trading convictions of hedge fund traders, they have tried doggedly to build a case against one of Wall Street’s most influential players: billionaire stock picker Steven A. Cohen.

On Tuesday, prosecutors appeared closer to that goal, charging a former portfolio manager at the hedge fund SAC Capital Advisors, a case that for the first time directly involves Cohen, the fund’s founder.