In Legend Quest, the spell casters that can learn the most via magic are the necromancers. With Book of Wishes, they have spells like séance, clairvoyance, past vision, spirit call, and spirit sense. These allow them to question the dead or see things that the caster never could have seen. But these types of spells should have their limits.
Take the past vision spell - It allows the necromancer to see through the dead person’s eyes in order to figure out the last thing(s) they saw as they were dying. Well, if you’re an assassin in this world, you should be aware that the “police” have spell casters who can do this, and you should assassinate your targets from behind. Simple, right?
But it begs the question: How much do the dead really know? If you spirit called the same person who was killed from behind, would his ghost have seen the scene as it floated up and out of his body? Could a spirit of the dead identify their killer, even if that killer was behind them? I say no.
I think that spirits should only be able to know what they knew in life. I have all these complicated reasons and theories, but basically in my game world, the soul has a bunch of parts. The part that the necromancer is talking to is not your “immortal soul” that goes on to heaven (or hell). It is more of a shadow of your life. In my world (at least) death magic doesn’t have the range to reach the heavens, but only the “shadow” part. So no divine intervention simply by casting spirit call.
This rule works pretty well in restricting the amount of information you can get from the dead. If they didn’t know it in life, they don’t know it in death. Also, if they wouldn’t tell you in life, why would they tell you in death? There are some pretty good reasons for that including desecration of the body, threatening living family, etc. But simply killing someone should not make them open up to you about everything. One would think the spirit might hate its attacker.