Lord Amherst (in 1763, under British colonial rule) is guilty -- but the U.S. Army in 1837 is innocent.
Interestingly enough, the well known painter George Catlin visited with and memorialized the Mandans just before they were almost wiped out by the smallpox epidemic. They are one of the best documented Indian groups. Besides, his paintings are gorgeous. We saw an extensive collection in D.C. year before last.
Medicine man Mah-to-he-ha in his ceremonial regalia.
Also, Americans were very interested in the Mandans. It was widely believed that they were descendents of Welsh who sailed to North American in the 11/12th century. Supposedly some had fairer hair and gray eyes.
I've read pros and cons about Amherst's guilt, but the letters I read seemed to indicate that he was guilty.