It is interesting how many casual (and even professional) historians confuse the issues of legal evidence and historical evidence.
I am reminded of this whenever I publish some primary source material that does not conform to prevailing storylines. There is a tendency to want to "quash" the evidence. The reactions tend to be inappropriately legalistic.
Last week's letter conveying Pinkerton's purported warning to the Democratic leadership in October 26, 1864 brought some interesting reactions. For instance,
State of mind arguments - statements from McClellan's circle can be discounted because of the group's prevailing "paranoia."
Credibility of the witness - very little of what Pinkerton ever said can be believed.
Corroboration - there were no witnesses to the meeting described and therefore the written statement of the meeting can be discounted.
Can you see the error in such reasoning? There is a distinction between discounting what is false, what is impossible, and what is unpalatable. One does not have the right to suppress what is suspect because it is distasteful. The historian's ethos demands that what is suspect be examined and discussed openly ... a major problem in most Civil War works published today. A point illustrated by the obscurity surrounding this purported Lincoln assasination plot alleged against the Democratic Party leadership.
Here is an interesting discussion on legal versus historical evidence.