To me, the reports that Ariel Castro celebrated the anniversaries of his captives' abductions, as if their abductions were a rebirth (into being buried alive in sex-slavery hell) are evidence of gratuitous cruelty and perhaps some sort of Satanic possession. In one of his lectures, Rudolf Steiner seems to have implied that it is possible to become effectively possessed by "unfolding" a sufficient amount of animosity in oneself (although he didn't elaborate on what he meant by "unfolding" - for all I know, it was an allusion to SRA), and Ariel Castro had an abundance of motivation for being mad at the world. His parents reportedly abused him, an uncle reportedly abused him sexually, and he was a school bus driver.
If Castro were possessed by some Satanic spirit, or "overshadowed" by the Spirits of Darkness, then the original "occupant" of his body, the spirit for which his body and soul were created, cannot be blamed for "his" crime, and the actual culprit is untouchable. His ability to keep this horror secret, and the fact that so many people missed clues that it was taking place, might also indicate that this situation was choreographed by the Spirits of Darkness, who have the power to plant ideas in people's minds. So, if someone were confronted with evidence of something amiss, the Spirits of Darkness could have planted an innocuous "explanation" in their minds, after which they would forget about Castro.
Perhaps a psychologist can provide a viable alternate explanation for these sick "birthday" celebrations, but this still wouldn't disprove my theory.