I had been so deadset on Mangan. Especially once the illusionist guy talked about two different illusionist tricks - once involving a confidant, and the other involving the illusionist mixing in with the stagehands. My belief was that Grimaud's daughter had been the confidant, and that after Mangan had committed the murder and (somehow) escaped he mixed in with the police, since they all saw him escape a different window and break in again. iirc it was even suspiciously mentioned that Mangan immediately opened the door as if he knew it was unlocked.
The why was obvious. Grimaud mentioned to Burnaby he would help him get with his daughter, so Mangan tried to kill him. Mangan (somehow) knew about Grimaud's past and killed Fley in some attempt to frame Burnaby (which is why Burnaby's light was on/there was blood).
I thought it seemed so perfect. Of course, I still couldn't explain how the murders were committed exactly. But I thought everything else seemed to fit so it didn't really matter how he escaped from the room.
The actual truth was crazy and quite brilliant, honestly. That said, the clock being ahead because of pure luck is kind of absurd. And the mirror thing, I just don't get that at all. I'd have to see it in person because it doesn't make much sense to me; it doesn't seem feasible.