Fenes said:
And of course, in a simulated world, treat the PCs like NPCs. If the nobles of a realm can get away with a crime, then so should the PCs, if they are powerful enough. So, in order to use the "Now suffer the consequences" approach, make sure you allow the PCs to bring the same amount of wrath down on their foes ("Ok... back when we had proof of the Duke killing his wife, why didn't he get smacked down with those ultra-NPCs? You said the duke was too powerful to be toppled over his wife's death, but if the king has these killers on call, how could that be? And if the duke has similar people on call, why are we still alive after investigating his wife's death?")
You're conflating power (level) with legitimacy (position in the feudal order -- I assume feudal since it's D&D and you said "Duke").
It's quite possible that being high level does not give a character greater "immunity" to behave obnoxiously (legitimacy is based on birth, or election, or the choice of the gods (as in Tibet), not the ability to kill stuff or how much money you have).
Or you could rule it that high level does get you legitimacy in your campaign/this particular country.
I see the question (for the DM) as: Is the campaign a world where a Sergeant who's tricky enough can take over and be dictator ruling by fear and the iron fist (1970s Uganda -- think Idi Amin) or is it a world where privilege is inherited and rank is sometimes given to powerful adventurers, but only when they respect and serve the legitimate ruler (Elizabethean England -- think Sir Francis Drake)? The D&D default is likely that both exist, but in different countries.
Also, you're conflating crimes against a person (the Duke murdered his own wife) with crimes against the state (the Duke murdered the king's arbiter). A state has a choice about whether to look the other way when a crime against a person is committed. (Ah, the Duke's kid beat up a vagrant again, but we need the Duke's troops for the war, so we'll ignore it.) But the state, if it wants to stay in business as a state, has no choice when it's authority is directly threatened. (The Duke tossed our arbiters down the well, in front of the populace? The secessionist devil! This means war!)
I'm talking about the difference between OJ Simpson killing his wife versus Timothy McVey blowing up the Federal Building in Oklahoma City. Both are murderers. One walked, the other was executed. The state (and the people) are annoyed by but can tolerate the first, and even if OJ had been convicted, execution seems unlikely. The second, there was no room for mercy -- McVey needed to die for attacking the nation, and indeed he did, quite swiftly compared to most death-penalty cases.
Max Weber, one of the fathers of political science, came up with the definition of the state that still works best:
"The state is the organization which holds a monopoly on the legitimate use of force within a given territory."
The PC's in this case not only commited illegitimate violence (murder of a person) but also directly challenged the state. As a poli sci/history major DM, I would make life very, very tough for a party foolish enough to think it's above the law, if they were in a place where there is a law/state. A state that kowtows to cop killers is no state -- and citizen cop killers are a much greater threat to the state (to its monopoly on power) than an external force like orc raiders killing random peasants.
You're singing:
"I shot the sheriff, but I did not shoot the deputy
I shot the sheriff, but I swear it was in self-defense
Arbiter John always hated me, why I do not know
But my level was higher, so I shot, I shot him down
And now he knows his place"
I'm singing:
"Bad boys, bad boys, what you gunna do?
What you gunna do when they come for you?
Policeman he give you no break
Not even the soldier man he give you no break"