He designed and built a hotel specifically to torture and kill his victims. The building featured trap doors, hidden staircases, secret passages, a crematorium, rooms without windows, chutes that led into the basement and a staircase that opened out over a steep drop to an alley. Some of his victims were meticulously dissected and the remains sold to medical universities.
Holmes feared some psycho might dissect him. After he was caught and sentenced, his final request was to be buried in concrete.