What if there was already a person inside the dark room (which would make sense, if the electricity was out...) waiting for Alfred? That's not really considered a trap, but a coincidence really.
After Alfred locked himself in the dark room, the person who was temporarily hiding inside had killed Alfred. Lucy had Alfred's original master key, and upon escaping the Surveillance room where Alfred unlocked the door, had unlocked the dark room from the outside with her master key, and then locked it.
...and something crazy! :O
Tina's corpse was, instead of being carried into the dark room, used dressed into a costume and used as a prop/puppet within the kitchen. Her body, although dead, was being held up by tools/an object (wires possibly) to give you the illusion of her levitation abilities.