Pulitizer Prize-winning historian Doris Kearns Goodwin knows the Kennedy family well. She has studied their role in American history — and she’s a longtime family friend.

But Goodwin still found plenty of surprises in the FBI’s file on the late Sen. Edward M. Kennedy, released Monday by the FBI.

Goodwin told WBUR’s Bob Oakes that the files deepen and complicate known stories about Kennedy’s life. She was stunned, she says, to see how many death threats the FBI had collected. “Knowing that his brothers had been killed, they weren’t simply vague threats,” Goodwin said....