The Manhattan U.S. attorney’s insider-trading crackdown has generated plenty of business for graying, distinguished members of the white-collar bar—and for the large, national law firms many of them call home. But when prosecutors went after Rengan Rajaratnam, the younger brother of imprisoned hedge-fund titan Raj Rajaratnam, the job fell to a relative newcomer, Daniel Gitner of the litigation boutique Lankler Siffert & Wohl.

Gitner succeeded where his predecessors all failed, steadily dismantling the complex case before it reached jurors and then persuading them to knock out the remnants on Tuesday after a speedy deliberation.