[Texas Eagle]

Kennedy escaped the car and then dove down in an attempt to retrieve Kopechne from the sunken Oldsmobile. Failing, he stumbled back to the cottage, where he enlisted Gargan and another friend in a second attempt to save Kopechne. The three men were unsuccessful; her body was not recovered. The trio then went to the ferry slip, where Kennedy dove into the water and swam back to Edgartown, about a mile away.

BS.

He went back to the party to tell his lawyer friends what happened and they formulated a plan to rescue Kennedy from prison.

[Col Frank Slade]

He needed 10 hours to formulate a story and sober up.

[Williams]

Key point is he went home, sobered up, put on fresh clothes and goes to the police the next day. Tells them calmly he left a girl to down the night before.