In my world one of the branches of magic is Sight; foresight, farsight and hindsight.
Foresight is basically the gift of prophecy. It's limited in that the world doesn't exist in a fixed timeline, so you can only see possible or probable futures. A very powerful Seer is dangerous and can see well enough to guide events, but someone of that power is rare.
Farsight does what it says on the tin; it lets you see things happening far away (technically anything happening at the present). It's useful only if you know where to look to see something important or relevant.
But Hindsight is where I'm having trouble. It's the ability to see visions of the past; true visions of events that actually happened. My issue is finding a way to limit this power. Unlimited it would basically mean committing a crime is practically impossible as any trained Seer would be able to see exactly what happened.
The only obvious limit I can see is time - The farther back you need to see the more power and skill is required. This provides a useful limit, but still means if your Seer Police arrive on the scene pretty quickly then you're scuppered.
The only other obvious counter is to use magic to obscure the Seer's power, which requires all crimes to be committed by or aided by a mage of some sort, which isn't helpful.
So in a medieval(ish) setting would crime still be possible if such a power existed?
What limits could I put on it, or what loopholes am I missing?
Obviously smaller communities wouldn't have trained Seers unhand, but presumably any lord time figure would make it his (or her) business to obtain the services of a Seer (which aren't going to be too uncommon) to aid in the execution of justice.