How about firsthand testimony that can be corroborated. If you’ve ever been in court for anything, it’s standard to not simply take whatever story you hear at face value.

So point to a story you’re saying is true, then show how it can be corroborated (by video? by documentation?). Show how there is no realiatic alternate explanation. Explain how your corroborated story amounts to genocide, and isn’t just a story about someone being arrested, for instance.