My guess is that the killer is the same person who said “Someone’s killing witches” in “A Taste of the Heights” and in the recap at the start of “Knightfall”.
From the Knightfall thread:
Regina had already been acting uncharacteristically smitten with Facilier, as if he had some magical influence over her judgement. Facilier is handsome and charming, but Regina is usually the queen of staying focused. Now Regina thinks she spent the night at Facilier’s. I wonder if that’s a false memory, implanted as a cover for some evil action. Did any coven members die around that time? Perhaps a body will turn up next episode.
I think the mysterious hand at the doctor’s murder will be revealed as Regina’s, operating under Facilier’s full voodoo control.
From what we’ve seen so far, the timing doesn’t work for Regina attacking the blind witch in the hospital, but I wouldn’t be surprised if Regina starts seeing flashes of memories that she can’t explain.
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