I read the book many years ago. The movie plays Ted in the best light possible. As if he had a sense of moral values or was introspective.
It also continues the myth they returned to the car to help the woman. Since they drove back to the site they had a jack and a jack handle to break the windows. They didn’t try. Even a large rock would have got that job done. Nobody went back to rescue her. Simply part of the story they created. And the movie repeats this myth.
I am convinced he wanted her dead: Dead women tell no tales.