Mathew Martoma, a former portfolio manager at billionaire Steven A. Cohen’s SAC Capital Advisors LP hedge fund, was sentenced on Monday to nine years in prison for engaging in what authorities called the most lucrative insider trading scheme in U.S. District Judge Paul Gardephe in New York also ordered Martoma, 40, to forfeit $9.3 million. Prosecutors accused Martoma of making illegal trades in pharmaceutical stocks based on tips about a clinical trial for an Alzheimer’s drug. They said those trades enabled SAC to generate about $275 million of illegal gains.