But a guy on the street who was there is ne’emon to tell you what he saw, experienced and was witness to. His testimony carries weight, whether in Bais Din or on the same street, far more than opinions of those who heard the story second-hand.
Books written l’acher hamaase rely on eyewitnesses, and, until they research ALL availabe evidence, and not only the side they feel ideologically biased toward, they are of little judgemental value.