There are lots of details to the Kennedy "story" (lie). I can still remember his national tv speech on this. He claimed to have tried to save her, he brought his cousin to the scene, and with his cousin standing there Teddy claims he jumped into the water and swam away into the night, risking his life a second time. he actually tried to make himself out the hero. And supposedly the cousin just went home (or back to the party?) and left Teddy presumed dead and the girl at the bottom of the channel, and told no one of this.
And remember that Kennedy money and lawyers prevented the inquest into her death from ever being completed. They demanded to be able to cross examine every witness, and they eventually gave the girl's family money.
Teddy showed up at the police station teh next day showered, sobered up, cool as a cucumber, with the girl still at the bottom. Totally disgusting.