Mary Jo Kopechne, was an American teacher, secretary, and political campaign specialist who died in a car accident at Chappaquiddick Island on July 18, 1969, while she was a passenger in a car being driven by U.S. Senator Ted Kennedy, it was the result of U.S. Senator Ted Kennedy's negligence and resulted in the death of his 28-year-old companion, Mary Jo Kopechne, who was trapped inside the vehicle, the event occurrence is known as what?