Davis was arrested in 1865. The government could had held a trial and convicted Davis, and then executed him if found guilty. Instead, they understood that to bring him to trial would validate secession (see Chase's statement above).
If Stanton had wanted Lee and Davis and the others hanged, they would have hanged.
It was Lincoln's words from the grave that saved Davis.
Chase plainly called all secession articles null and void, and said that the perpetual Union of the Articles was made more perfect by the Constitution. His position on Davis was based on double jeopardy, not the total BS you present.
Walt
I guess when you rule by the sword rather than by law you can do pretty much what you want to. You would have loved the U.S.S.R.