An Alzheimer's expert says he was too ashamed to be truthful when the FBI confronted him with claims he fed inside information to a hedge fund manager.

Sidney Gilman described his dealings with investigators Tuesday to a Manhattan jury at the trial of former SAC Capital portfolio manager Mathew Martoma. The government says the secrets were about a clinical trial for a promising Alzheimer's drug.

The 81-year-old Gilman says he was "hoping it would go away" when he lied to the FBI in September 2011. He says he had betrayed his colleagues, himself and his employer: the University of Michigan. He eventually signed a non-prosecution agreement and agreed to testify.

Prosecutors say Gilman's tips helped Martoma and SAC Capital earn a quarter billion dollars illegally.

Martoma has pleaded not guilty.