While I'm certainly no expert on occult-related crime, and know only the basics in such Christian esoterica as angelology or demonology, I was probably as good as he was going to find in the department, as no one here that I know of has any real background in such fringe material. (My department chair laughed at me when I told him about this a few minutes ago: telling me that I'd made a mistake in signing up with the university for media requests; I had thought that that was just expected of us, but he then explained how he trimmed down his list of what he was available for to very specific topics, because apparently Religious Studies does tend to draw the fringe of the press's concerns. This precaution apparently didn't stop the production company for My Name Is Earl from calling to consult him on whether their use of a tag line in their advertising about "karma" was acceptable....) So I talked about the Christian conceptions of good and evil with this guy, clearly giving him more to process than he expected when I tried to explain that yes, we believe in evil but that, technically speaking, we don't believe it actually exists, as such. (You've never seen an evil tree, stepped in a big pile of evil walking home from work, etc.)
This understanding is weightily described in the old 1913 Catholic Encyclopedia that you can find online:
It is evident again that all evil is essentially negative and not positive; i.e. it consists not in the acquisition of anything, but in the loss or deprivation of something necessary for perfection. Pain, which is the test or criterion of physical evil, has indeed a positive, though purely subjective existence as a sensation or emotion; but its evil quality lies in its disturbing effect on the sufferer. In like manner, the perverse action of the will, upon which moral evil depends, is more than a mere negation of right action, implying as it does the positive element of choice; but the morally evil character of wrong action is constituted not by the element of choice, but by its rejection of what right reason requires. Thus Origen (In Joh., ii, 7) defines evil as stéresis [I'd call that "privation" or "deprivation" in English]; the Pseudo-Dionysius (De Div. Nom. iv) as the non-existent; Maimonides (Dux perplex. iii, 10) as "privato boni alicujus" [Latinists help me out: I think that's something like "privation of all good"? It's been over a decade since I had to really work in Latin]; Albertus Magnus (adopting St. Augustine's phrase) attributes evil to "aliqua causa deficiens" (Summa Theol., I, xi, 4) [I think that's something like "being deficient in some fashion"?]; Schopenhauer, who held pain to be the positive and normal condition of life (pleasure being its partial and temporary absence), nevertheless made it depend upon the failure of human desire to obtain fulfillment--"the wish is in itself pain". Thus it will be seen that evil is not a real entity; it is relative. What is evil in some relations may be good in others; and probably there is no form of existence which is exclusively evil in all relations, Hence it has been thought that evil cannot truly be said to exist at all, and is really nothing but a "lesser good." But this opinion seems to leave out of account the reality of human experience. Though the same cause may give pain to one, and pleasure to another, pain and pleasure, as sensations or ideas, cannot but be mutually exclusive. No one, however, has attempted to deny this very obvious fact; and the opinion in question may perhaps be understood as merely a paradoxical way of stating the relativity of evil.