I disagree. The problem is that Garagan and the other guy left the party. They left because Fat Head Ted was in the driveway, after the crash. They tell partial truths, but I think the main story is Ted was going to the beach for some hanky panky, saw a police car and hit the gas. He didn’t want a DUI arrest with a girlfriend, for his wife to see in the papers. The cop watched the car speed away.
I think he was in the accident, and after feeling all that water inside the car, he figured she was dead.
Then he hoped his two buddies would cover for him, and say they never left the cottage and knew nothing, and that Mary Joe just drove off the bridge alone. But his two buddies had witnesses back at the cottage that would trip them up, so they couldn’t lie.
OK, but I think that scenario is a tad too convoluted.
I think they left the party unseen with the intention of having ‘fun on the beach’. They did so, upon making their way back they saw Deputy Luke, panicked because he was DWI so he told her to drive back to the cottage alone while he swam across to Edgartown and, thus, her absence, if even known by the others by then, would be covered by her having had to take THoC to the last ferry of the day.
Ultimately, we’ll never know for certain what actually happened that night save a girl died in THoC’s mommy’s car.