Agent Theodore Cacioppi (KAH'-choh-pee) testified Monday.
He was watching television at home on Dec. 10, 2008, when his supervisor contacted him. The supervisor told him that the FBI had developed information that Madoff might be running the biggest Ponzi scheme in history. He and other agents interviewed Madoff the next morning for an hour before arresting him.
Months of testimony are expected at the Manhattan fraud trial. Opening statements were last week.
The ex-workers are accused of helping Madoff cheat thousands of investors out of billions of dollars. Their attorneys say they were duped just like Madoff's clients.
Madoff is serving a 150-year prison sentence.