H. H. Holmes was the first recorded American serial-killer, at least in the sense we now associate the word - he was active in 1893 and confessed to over 27 murders, though his true body count may of been considerably larger.
H. H. Holmes is especially infamous for designing a "castle" which was overrun with many rooms designed to torture and kill his unwitting victims, the design of this structure was as ingenious as it was evil and Holmes was said to have hired numerous workers in the building of it so that only he would know the full layout of the terrible maze.
Holmes was hanged on May 7th, 1896 and was granted his final request to be buried in concrete to prevent people digging up and dissecting his corpse, as he had done to many of his victims.