First, he's under no obligation to archive his posts. It's on the world to archive them and prosecute the perpetrators of the documented crimes.
Second, the platform in question has, at the highest levels, intelligence officers from the entity committing those crimes.
Third, humanity has failed in its moral duty yet again, and this sort of "neutral" commentary that ends with a glib remark directed at a murdered non-combatant is shocking to the conscience.