This is vexxing me. I am vexxed. I am a lawyer, so I thought about this way harder than I should.
So, assuming our wizard is not working for the government, no warrant would be needed. (If there are wizard cops we have bigger problems).
The situation is akin to a someone with a telescope. Possibly illegal, possibly not, depends on what you were doing and why. Either way, if you come forward of your own volition, then we turn to whether or not you were able to see what you claimed to see, and in both cases, it hinges on the equipment in question.
If you claimed to see something happening half a mile away, we need to ascertain whether the equipment you used to do it allowed you to do that. Unlike with the telescope, which once we understand you used one, we know how it works, we have no way of knowing how the wizard orb functions.
Can it pick up on someone's violent thoughts, and possibly be showing us their mental image? Can it show you things that aren't happening? Potential things that are happening? Alternate realities?
In any of the situations above, it can't be used as evidence, because we have no way of proving it wasn't a violent fantasy/alternate reality/metaphor for something ominous heading your way via eldrich horror.
Lets say that its 100% accurate to reality. Can you control what it shows? (Also, if you can, how did you stumble on the murder?) If you can't, you might be able able to use it as evidence, but you'll face some issues. More on that later.
Ok, so you are an eye-witness who claims to have seen a murder. That's relevant testimony in the case. Now, getting the court to accept that the orb: 1. Does what you say it does, 2. Allowed you to view a murder in a manner you otherwise wouldn't be able to would be incredibly tricky (although less so if you could do it on command). The hardest part would be getting the judge to agree to a pre-trial hearing about whether or not the orb let you do this without bursting into laughter, but if you got that hearing it would be pretty straightforward to get it admitted, provided you could show everyone that the orb works as advertised.
There would also be the option of idk, lying about how you saw it (I was looking through the window/I was walking my dog nearby)
Or and I can't believe this isn't the first course of action, you could skip going to court and just curse the murderer because you are a wizard with a magic orb!
