There is a book out called “Misquoting Jesus”. I forget the name of its author. I saw a number of interviews with him as he was on his plug-my-book tour of TV shows. He was a born-again christian who was so enthusiastic about his faith that he decided to find the oldest known versions of the bible to be able to read them and know for himself what they said. He even learned ancient Greek so that he could read them himself, rather than rely on a translation from someone else.
He found that many things that we take for granted in the bible were not in those older copies. Many of these parables were hand-written into margins obviously later than the manuscripts were originally written. One of those had to do with casting the first stone.
So, although the story is a really good one, it was not recorded in the earliest versions of the bible. Did it really happen? Does it matter? We report; you decide.