What an uncanny coincidence! There is a discussion on another message board this very minute about the rights issues concerning the original musical elements/master tapes for Elmer Bernstein's iconic score. Apparently the estate of one of the film's producers (possibly that of Alan Pakula or of Robert Mulligan?) is blocking a respected label from putting out a true, no-doubt-about-it soundtrack of the To Kill a Mockingbird score. I guess the Gregory Peck estate is off the hook.
Here's a fact I did not know. The esteemed composer John Williams is the one playing the piano in the opening scene of the film and throughout the movie.
That reminds me that Leonard Bernstein himself is the guy playing the piano on the original soundtrack of his score for the On the Waterfront film.