That being said, the US Congress and Courts found him NOT GUILTY. The charges were dropped. To carry on as otherwise is petty and even slanderous of the will of our Nation.
Since Davis never came to trial the how could the courts have found him not guilty? And when did Congress weigh in on the matter?
I'm sorry, but I do seem to recall this little nagging fact... Sumpter was armed and given time to clear out. It did not.
Federal property on Confederate ground is "off sides"
And since when is appearance in court an aspect of law?
You have trials, and the right to represent yourself. Nothing required unless the judges demands it.