You are correct that the sterile fact is the south did fire first. That was Lincoln intentions to provoke a war and make the South look like they started it. And it worked. Just read any of our so called present day "History Books" for confirmation.

But "sterile facts" alone do not always determine guilty. I would hate to be in court defended of committing a capital crime and use only the sterile facts of the case as my defence without the Judge considering the provacation and extenuating circumstances. The provacation and circumstances, the "why did you do it," are always a point of any defence of someones actions. Many a court case has been reduced from Capital Murder to Justifiable Homicide because of the circumstances under which the death occurred.

The whole justification for the Union War against the Southern States was the simplistic "sterile fact" that the South fired the first shot at Fort Sumter.