There was a traditional type of eyewitness, whether it was a survivor or a fellow perpetrator, who actually saw specific events at hand. We also used and in this case survivor witnesses who may not have, probably in many cases -- most cases, didn't know the defendant, had no idea what the defendant did, but could talk in general about what his or her perception of what the guards were doing was, and also more important, what life was like. There's no one, no book, no perpetrator testimony, no historian, can possibly get across with the same intensity as a survivor talking what it felt like to the survivor, and when the survivor talks, in that sense, if one accepts the testimony as being no more than what it is -- that survivor's memory -- some of the inaccuracies that inevitably come up in human memory, even when they can't be reconciled with an explanation, still don't detract from the image of what life was like in a concentration camp, or in a line waiting to be shot at a pit. That this is something that this kind of testimony lends an immediacy that the dry documentation just can't give.