That fateful night, as he studied the cycle of souls, he was struck by the realization that he, like the original golem, had materialized with clarity and without preamble into this realm, a blank soul awaking inside a physical form that felt so foreign to him as to be repulsive.
He believes himself to have aquired the soul of the original golem. Also, if Katherine's theories are true he may have simply "tuned-in" the frequency.
