So, I assume he has Ghost Speaker.
A couple of things:
-
If the ghost is present, he might not be able to convince it to tell him what's going on. Or maybe the ghost is insane and rattles off clues instead.
- Or maybe the victim didn't see his murderer...or maybe he points to the wrong person(the murderer was disguised or mimicked or it was dark).
- Maybe they have to
find the ghost first. That would involve summoning the ghost, which requires a link.
- Maybe something ATE the ghost. That happens.
Just as a warningI don't know if I'd make it too hard, though. Being able to speak to a person's ghost and find out who the murderer
should be a definite advantage. And I wouldn't try too hard to block his character from using his strengths. Feel free to complicate things, but let him use his powers to his advantage.
I think it would be cool for him if he could just skip the whole investigation and move on to finding the murderer. As long as it's cool - you could even make it a social conflict.
Now the adventure becomes finding the murderer - or proving the person murdered the other. You can't just tell the police you talked to the murderer's ghost. You still need proof. So now the adventure changes from finding out who the murderer is to capturing and/or finding legitimate clues. Knowing who the murderer is just points them in the right direction.
Maybe the murderer is someone with political clout. It could be tricky.
Lastly, if he has Ritual(ectomancy), he can do anything a regular Mage with Thaumaturgy can do: skill replacement for Contacts, burglary, investigation, empathy etc...etc...etc...
As long as it involves ghosts, so he
should be able to make the investigation part quicker. Honestly, that may be an advantage to your game.
Regarding Complications:
Depending on his aspects, especially if he's new at ectomancy, you can have him accidently summoning malevolent creatures or things that lie. Give him a FP.
If we knew the situation, people could give more specific advice.
Hope that helps a bit...
EDIT: I have a character with Ghost Speaker and it's been
nothing but a headache