On July 18, 1969, Kopechne attended a party on Chappaquiddick Island, off the coast of Martha's Vineyard, Massachusetts, held in honor of the Boiler Room Girls. It was the fourth such reunion of the Robert Kennedy campaign workers.[10]
Kopechne left the party at 11:15 p.m. with Robert's brother Ted Kennedy, after he ? according to his own account ? offered to drive her to catch the last ferry back to Edgartown, where she was staying, even though John Crimmins, Ted Kennedy's part-time driver was present at the time she reportedly asked to leave. Kennedy stated he made a wrong turn on the way and came upon a narrow, unlit bridge without guardrails. Kennedy drove the 1967 Oldsmobile Delmont 88 off the bridge and it overturned in the water. Kennedy extricated himself from the submerged car but Kopechne died, after what Kennedy said were several diving attempts to free her.[5]
Kennedy contacted several aides that night, but failed to report the incident to the authorities until the car and Kopechne's body were discovered the next morning.[5] Kopechne's parents said that they learned of their daughter's death from Ted Kennedy himself[1] before he reported his involvement to the authorities, but that they learned Kennedy had been the driver only from wire press releases some time later.[3]
A funeral for Kopechne was held on July 22, 1969, at St. Vincent's Roman Catholic Church in Plymouth, Pennsylvania, attended by Kennedy.[11] She is buried in the parish cemetery on the side of Larksville Mountain.
A week after the incident, Kennedy pleaded guilty to leaving the scene of an accident after causing injury. He received a two month suspended sentence.[5] On a national television broadcast that night, Kennedy later said he was not driving under the influence of alcohol nor had he engaged in any immoral conduct with Kopechne.[5]
The Chappaquiddick incident and the death of Kopechne became the grist for at least fifteen books, as well as a fictionalized treatment by Joyce Carol Oates. Questions remained about Kennedy's timeline of events that night, about his actions after the accident, and the quality of the investigation and whether official deference was given to a powerful politician and family.[12] The events surrounding Kopechne's death damaged Kennedy's reputation and are regarded as a major reason that he was never able to mount a successful campaign for President of the United States.[13]