Incidentally there's a pdf book here: The Murder of Little Mary Phagan (300+pp, 2 facing, 15.4 Mb). It says that Fiddlin' John Carson was singing The Ballad of Mary Phagan (not The Grave ... song) outside the courthouse at the end of the day (I don't know if that's mythical or not) and gives the words for that song.

Mick