I am going to GM a session this week that will likely end with the players wanting to prosecute a hermetic magus for breaking the code. That will be the first time this happens for me and I would like to ask some advice.
My group is playing in the Triamore setting.
A few sessions ago the players made a deal with the Duke of Brabant that he would support them against Etienne de Gaumond and hold them free of various taxes, in return for a longevity ritual and more importantly that they would support him politically as a vassal and counsel him in matters of magic, this agreement is not public knowledge!.
The Duke(Henry) has a problem that a well liked local mystic/hedge wizard (Aelfric) has been killed and he suspects that there was magic involved somehow.
In fact what happened was that a magus by the name of Flavius of Flambeau found Aelfric and offered him to join or die, and it ended poorly for Aelfric. Flavius did not make much of this killing and made no attempts to hide his deed. Mundane authorities cannot find him because he is essentially a murder-hobo who lives far away and he doesnt really know anyone in the area. But InVi spells will determine his sigil very easily.
If the players identify the Flavius to the duke Henry he will charge Flavius with murder and have him declared an outlaw if he doesnt show up for trial (which he wont).
There are some snags though.
First, the killing took place in the Normandy Tribunal, and Flavius is resident there too. But the players are based in the Rhine tribunal, and the Duke Henry is also based in the Rhine tribunal.
Second it is not entirely obvious to me that the players have a case. What they could do is try to argue that since Henry came to them asking for assistance, this constitutes mundane interference, because it caused inconvenience to the players. Could this work? What sort of legal angle could they try to pursue? What are the likely legal arguments that the players could pursue and what are the likely arguments that could be used against them?
However according to hermetic law the killing of Aelfric is entirely within the bounds of the code, as Flavius did offer him to join before killing him. He didnt ask very nicely and was surely hoping for an answer of "or die" but that is kind of besides the point. The reason why Flavius was there in the first place was to claim a vis source owned by Aelfric, but Flavius is not going to tell that to anyone.
Is it possible that Flavius could countersue and argue that the players have caused him trouble with the mundanes by making his identity known to the duke of Brabant resulting in him being declared an outlaw, where he would otherwise have suffered no consequences?
I am assuming that the players will be wise enough to not admit that they have deal with the duke Henry to assist him with magical problems, as they would otherwise open themselves up to all sorts of trouble.