This is a purely British legal reply.
There is no obligation to interfere in a crime. There is no obligation ro rescue a drowning person. There is no obligation to endanger yourself if you see a crime in progress. There's an obligation to stop and speak to a police officer if you are instructed to do so, but there's no obligation to call the police in the first place.
If your PC is nto a good PC, I wouldn't penalise them. If they are good, I might give them a speaking to; perhaps a vision from a god if they're a cleric. If they're a paladin, I'd come down on them like a ton of bricks. Paladins, and the whole 'higher standard' nonsense... (I might not ex-paladinize them, but would certainly drop a lot of hints, and slowly strip powers until he or she atoned).
This act is, in my mind, pretty immoral in-game, mind you...
arcady said:
What if afterwards, the PC tried to stabalize the victim? Does that change anything over letting the incident happen without even shouting out an alarm?
If this was a sign of remorse or something, I'd be inclined to let the entire incident slide, but keep my eyes open for roleplaying opportunities.
arcady said:
What if the PC was following the victim, and witnessed the entire event from start to finish?
In-game, I don't think this has any bearing. PCs follow people for all sorts of reasons, and the PC in question might have planned to mug the victim themselves!