As far as first-hand accounts are concerned, for that matter eyewitness testimony (because they're basically the same thing), this article demonstrates why the testimony itself is not really a good source to rely upon alone- because of the human memory issue (not including the common social knowledge aspect of intentional dishonesty with testimony):
http://agora.stanford.edu/sjls/Issue...er&tversky.htm
Another interesting article:
http://www.visualexpert.com/Resource...essmemory.html