> It really hit me when I realized that there are only two ways to prove intent: The criminal admits it, or the prosecution proves that there are literally zero other possible explanations that could possibly fit the actions.

I doubt we'll have absolute certainty about genocide until Nuremberg-style trials take place. The problem is such trials won't happen unless the international community intervenes, and they don't seem willing to intervene without 100% certainty. Chicken-egg problem.