one of the principles of our legal system is that justice isn’t retroactive
There have been plenty of cases in history where this didn’t hold.
King Charles I of England. King Louis XVI of France (not to mention the rest of his far-less-culpable family). Many prominent Nazis post-WWII. When society collectively decides that someone’s actions were heinous enough and caused enough harm, at a certain point a law can be created and applied retroactively, often on the grounds that there was a clear violation of some greater principle that should be self-evident.
I like how you missed the “our legal system” when giving examples entirely outside the legal system in which this killing took place.
Umm, no, not really? King Louis maybe, but the Common Law system used across most former UK colonies traces a line back to before King Charles’ execution, and the Nuremberg Trials were set up by the Allies (which prominently includes the US and UK) and form an important basis of 21st century international law.
