There are several studies as to what actually happened but the most credible are that Ted wasn’t in the car at all. He had got Mary Jo drunk and was planning to make out with her in the car when they were spooked by a passing police car on the island. Ted hid in the bushes while MJK tried to drive the unlit road to the bridge where it flopped off the edge of the wooden bridge and into the water.
Ted returned to the party house and asked some aides to drive him home but it was now after midnight when the ferry stops running so he jumped from the pier where the ferry stops and swam the shallow waters back to his motel room.
According to witnesses, he was calmly enjoying breakfast the next morning when aides reached him and informed him about MJK. The witnesses said he turned pale at the news.
He now had to concoct a story to explain how he could have left the party with a women who drowned without drowning himself yet could be presented in a way that did not hint of infidelity. He relied on his aides to support his story.
That’s when the neck brace showed up and the belated reporting to the police.
On arriving at the party house, Kennedy told his cousin Joe Gargan exactly what happened. Joe went back to the Dyke Bridge with Ted, but they could not find any trace of Mary Joe. (It late at night and dark.)
Ted wanted Joe to frame an alibi, but he refused. He wanted Joe to say that Mary Jo had taken the car and driven off by herself. Joe refused to cooperate. He wanted to call the police immediately. Ted said he would call the police when he got back to his hotel in Eagartown, which was a across a small channel from Chappaquiddick. Joe reluctantly agreed and drove Ted to the Ferry slip where it was a short swim back to Eagartown.