I'm afraid I can't remember! It was 20 years ago - I think they did do it onstage, on benches, but I can't remember anything more useful than that. It's offstage in the original play, (I think - god my memory!), but I've read a note that says Wajda's 70's stage production seated the Tribunal in the audience, so I presume, as with the film, he added it from the surviving trial notes.