This would be a pretty good post for fantasywriters!
Think about it carefully, especially with mental magic.
I think some authors are intimidated by the consequences of mental magic when it comes to the law, and try to avoid it with justifications that seem kind of flimsy. But if you think about it, even if you know the facts of a crime that occured, there can still be many other questions to settle, such as what a just punishment would be. (According to that society's rules.) If you need a trial you can have one.
I used to have telepaths in my cheesy urban fantasy verse, but they got in the way of everyone being confused about what was going on, so I got rid of them.
I'd like to see what kind of limitations could be introduced on mental magic. Distance, or passage of time dimming the impressions, or a question of reliability (maybe retrocognition is as hard to trust as precognition, for whatever reason), or sheer difficulty to translate (despite having used it myself, I don't think someone with telemetry could actually get perfect impressions of other humans from objects; how objects "perceive" humans is obviously going to be different from how humans do). But too often, just as with the god who has to be omniscient or powerless, the assumption seems to be that mental magic is perfectly clear or perfectly wayward.
I'd like to see what kind of limitations could be introduced on mental magic.
Maybe the mage feels whatever emotions the people around him feel. So, if the mage is talking to a friend, and an angry person walks by, the mage gets angry at his friend. It would cause the mage to have mood swings, which would drive away people. So, that mage would have a pretty bad social life.
Apologies for coming along years late, but here's the limitations I use for telepathy when it comes to gathering evidence and such: the telepath can only see what the victim is able to remember. Memories aren't usually very high fidelity, and they tend to focus on a few objects, so a witness to a murder may only be able to remember that the murderer was wearing a red shirt and was tall. They work wonders as lie detectors, with the caveat that they can only detect conscious lies (if a person has managed to completely convince (him/her)self of an alternate version of what really happened, then that's what a telepath will see as truth.