For a show that once included Anne Frank and aliens in the same season - and still never really explained either, BTW - American Horror Story: Hotel's reveal of the 10 Commandment Killer's identity was surprisingly simple.
Following the suicide of the Countess' creepy blonde daughter Wren, John (Wes Bentley) arrives at the Cortez demanding answers. Sally reluctantly agrees to show him where the 10 Commandments Killer has been hiding: Room 64, the same room where John's been staying.
Still not connecting the dots, Sally leads John to the secret room behind the armoire that's filled with mementos of the killer's victims dating back to 1926. Still not connecting the dots, John continues to babble on along the lines of "Who let the killer in my room?" until Sally spells out what we've all known for weeks: John himself is the 10 Commandments Killer.
Upon this realization, all the memories from John's blackouts begin to flood back. But the flashbacks don't stop there. We learn that John first arrived at the Cortez in 2010 after a particularly grisly day at work. He soon winds up crashing Mr. March (Evan Peters) and the Countess' (Lady Gaga) monthly dinner, which makes March absolutely furious until he notices John's black aura and penchant for being casually macabre. March promptly gives his ex-wife the boot and begins courting John to be his protégé.
Maybe it was the liquor or maybe it was the liquor combined with his mental instability, but John is soon talking freely about his rage and disillusionment with the justice system. Knowing John still isn't ready to go full psycho cop, March enlists the Countess to abduct Holden to push him over the edge. After the loss of the only child he truly loves — because clearly neither he nor Alex (Chloe Sevigny) give a crap about Scarlet — John continues going to the hotel, visiting Mr. March and eventually striking up an affair with Sally (Sarah Paulson). Thinking it was finally time, March shows John his trophy room, which is just a cramped, unlit hallway filled with taxidermy animals and the head of an accountant.
Clearly having some semblance of rationality remaining, John runs away and never looks back. At least until he fails to get a few convictions and runs right back to the Cortez in 2015, finally ready to pick up where Mr. March left off.
Back in the present, John goes to the morgue and begins confessing all of this to his cop friend who doesn't believe a word of it. The joke's on the cop though, since John immediately murders him for coveting Alex. This means there are only two murders left until John and March's nearly century-long 10 Commandments murder project is complete, but five episodes to go until the season finale. Hopefully, we just won't have to wait too long until John and Alex admit to each other they're both monsters and terrible parents.