Wikipedia is a good place to start looking for information when you have a topic you don't know about, but you should use it to find other sources, not as your only source.
I am sorry. I suppose to post it here last night. I was in bed. I found a wiki to copy and paste it here.
Chappaquiddick incident
Main article: Chappaquiddick incident
The Chappaquiddick incident refers to the circumstances surrounding the 1969 death of Mary Jo Kopechne, a former staff member in Senator Robert F. Kennedy's 1968 presidential campaign. Edward Kennedy was driving a car with Kopechne as his passenger when the Senator drove off Dike Bridge into Poucha Pond between Chappaquiddick Island and Cape Poge barrier beach. The Senator swam to safety, but Kopechne died in the car. Kennedy left the scene and did not call authorities until after Kopechne's body was discovered the following day. He pleaded guilty to leaving the scene of an accident and was sentenced to two months in jail, suspended.
In January 1970, an inquest into Kopechne's death took place in Edgartown. At the request of Kennedy's lawyers, the Massachusetts Supreme Judicial Court ordered the inquest be conducted in secret.[20][21] Judge James A. Boyle presided over the inquest. His conclusions were as follows:
* "Kopechne and Kennedy did not intend to return to Edgartown" at the time they left the party.
* "Kennedy did not intend to drive to the ferry slip".
* "[Kennedy]'s turn onto Dike Road was intentional".
Judge Boyle also said that "negligent driving appears to have contributed to the death of Mary Jo Kopechne".[21]
Under Massachusetts law, Boyle could have ordered Kennedy's arrest, but he chose not to do so.[21] District Attorney Dinis chose not to pursue Kennedy for manslaughter.
I am little confuse because you said it's accident. My mom told me about Kennedy didn't rescue Mary from drown.