If I may butt in on this debate: An Honorable Defeat by William Davis, pg 386.

...........on Dec 5, 1868 the chief justice of the US dismissed the treason indictments, declaring that since Davis had already lost the right to hold any state or federral office, therefore already been punished, and any further trial would be a violation of the ex post facto statute.

Page 384: ...............none of the captured leaders, not even Davis, had been among those who brought about sucession. (therefore they were not treasonists)