In general, it works far better to Amnesia someone just before killing them (resurrections take 10 minutes, and you must be dispelled within 10 minutes for the Amnesia to be gotten rid of). If you mess it up and can't Amnesia them, and then run to the Earth circle and hope they res, you will probably be disappointed to find that Spirit viewing that circle as "hostile" and resurrecting someplace where you aren't.
But if they DO happen to resurrect there, you still have to worry about the person performing the resurrection, plus getting into the circle to attack your victim a second time, then you have to get out of the circle. If you're able to do that, you'll likely have to amnesia the person recognizing you in/out, assuming they even let you out (a circle is a great jail).
Even then, you'd still have to worry about them being Dispelled within 10 minutes; characters know they have been Amnesia'd, and I've seen characters ask to be dispelled even after they res, "just in case".
You could have an accomplice, of course, to let you in/out of the circle, or even administer the Amnesia in your absence to an unsuspecting victim, but you should probably trust them. A lot.