First Modern American Serial Killer, Dr. Henry Howard Holmes

This is a terrifying story from Wikipedia:

Herman Webster Mudgett (May 16, 1861– May 7, 1896), better known under the alias of Dr. Henry Howard Holmes, was one of the first documented American serial killers in the modern sense of the term. In Chicago at the time of the 1893 World's Fair, Holmes opened a hotel which he had designed and built for himself specifically with murder in mind, and which was the location of many of his murders. While he confessed to 27 murders, of which nine were confirmed, his actual body count could be as high as 250. He took an unknown number of his victims from the 1893 Chicago World's Fair, which was less than 2 miles away from his "World's Fair" hotel.

The case was notorious in its time and received wide publicity through a series of articles in William Randolph Hearst's newspapers. Interest in Holmes's crimes was revived in 2003 by Erik Larson's The Devil in the White City, a best-selling non-fiction book that juxtaposed an account of the planning and staging of the World's Fair with Holmes's story.

Chicago and the "Murder Castle"

While in Chicago during the summer of 1886, Holmes came across Dr. E.S. Holton's drugstore at the corner of S. Wallace and W. 63rd Street, in the neighborhood of Englewood.With Holton suffering from cancer, his wife minded the store.Holmes got a job there and then convinced Mrs. Holton to sell him the store. They agreed that she could still live in the upstairs apartment even after Holton died. Once Holton died, however, Mrs. Holton mysteriously disappeared. Holmes told people that she was visiting relatives in California. As people started asking questions about her return, he told them that she was enjoying California so much that she had decided to live there.
Holmes purchased a lot across from the drugstore, where he built his three-story, block-long "Castle"—as it was dubbed by those in the neighborhood. It was opened as a hotel for the World's Columbian Exposition in 1893, with part of the structure used as commercial space. The ground floor of the Castle contained Holmes's own relocated drugstore and various shops, while the upper two floors contained his personal office and a maze of over one hundred windowless rooms with doorways opening to brick walls, oddly angled hallways, stairways to nowhere, doors openable only from the outside, and a host of other strange and labyrinthine constructions. Holmes repeatedly changed builders during the construction of the Castle, so only he fully understood the design of the house, thus decreasing the chance of being reported to the police.

After the completion of the hotel, Holmes selected mostly female victims from among his employees (many of whom were required as a condition of employment to take out life insurance policies for which Holmes would pay the premiums but also be the beneficiary), as well as his lovers and hotel guests. He tortured and killed them. Some were locked in soundproof bedrooms fitted with gas lines that let him asphyxiate them at any time. Some victims were locked in a huge soundproof bank vault near his office where they were left to suffocate. The victims' bodies were dropped by secret chute to the basement, where some were meticulously dissected, stripped of flesh, crafted into skeleton models, and then sold to medical schools. Holmes also cremated some of the bodies or placed them in lime pits for destruction. Holmes had two giant furnaces as well as pits of acid, bottles of various poisons, and even a stretching rack. Through the connections he had gained in medical school, he sold skeletons and organs with little difficulty.

Capture and arrest

Following the World's Fair, with creditors closing in and the economy in a general slump, Holmes left Chicago. He reappeared in Fort Worth, Texas, where he had inherited property from two railroad heiress sisters, one of whom he had promised marriage to and both of whom he murdered. There he sought to construct another castle along the lines of his Chicago operation. However, he soon abandoned this project, finding the law enforcement climate in Texas inhospitable. He continued to move about the United States and Canada, and while it seems likely that he continued to kill, the only bodies discovered that date from this period are those of his close business associate and three of the associate's children.
In July 1894, Holmes was arrested and briefly incarcerated for the first time, for a horse swindle that ended in St. Louis. He was promptly bailed out, but while in jail, he struck up a conversation with a convicted train robber named Marion Hedgepeth, who was serving a 25-year sentence. Holmes had concocted a plan to swindle an insurance company out of $20,000 by taking out a policy on himself and then faking his death. Holmes promised Hedgepeth a $500 commission in exchange for the name of a lawyer who could be trusted. He was directed to Colonel Jeptha Howe, the brother of a public defender, who found Holmes’s plan to be brilliant. Holmes's plan to fake his own death failed when the insurance company became suspicious and refused to pay. Holmes did not press his claim; instead he concocted a similar plan with his associate, Benjamin Pitezel.
Pitezel had agreed to fake his own death so that his wife could collect on the $10,000 policy, which she was to split with Holmes and the shady attorney, Howe. The scheme, which was to take place in Philadelphia, was that Pitezel should set himself up as an inventor, under the name B. F. Perry, and then be killed and disfigured in a lab explosion. Holmes was to find an appropriate cadaver to play the role of Pitezel. Holmes instead killed Pitezel. Forensic evidence presented at Holmes's later trial showed that chloroform was administered after Pitezel's death, presumably to fake suicide (Pitezel had been an alcoholic and chronic depressive). Holmes proceeded to collect on the policy on the basis of the genuine Pitezel corpse. He then went on to manipulate Pitezel's wife into allowing three of her five children (Alice, Nellie and Howard) to stay in his custody. The eldest daughter and baby remained with Mrs. Pitezel. He traveled with the children through the northern United States and into Canada. Simultaneously he escorted Mrs. Pitezel along a parallel route, all the while using various aliases and lying to Mrs. Pitezel concerning her husband's death (claiming that Pitezel was in hiding in South America) as well as lying to her about the true whereabouts of her other children—they were often only separated by a few blocks. A Philadelphia detective had tracked Holmes, finding the decomposed bodies of the two Pitezel girls in Toronto. He then followed Holmes to Indianapolis. There Holmes had rented a cottage. He was reported to have visited a local pharmacy to purchase the drugs which he used to kill Howard Pitezel, and a repair shop to sharpen the knives he used to chop up the body before he burned it. The boy's teeth and bits of bone were discovered in the home's chimney.
In 1894, the police were tipped off by his former cellmate, Marion Hedgepeth, whom Holmes had neglected to pay off as promised for his help in providing Howe. Holmes's murder spree finally ended when he was arrested in Boston on November 17, 1894, after being tracked there from Philadelphia by the Pinkertons. He was held on an outstanding warrant for horse theft in Texas, as the authorities had little more than suspicions at this point and Holmes appeared poised to flee the country, in the company of his unsuspecting third wife.
After the custodian for the Castle informed police that he was never allowed to clean the upper floors, police began a thorough investigation over the course of the next month, uncovering Holmes's efficient methods of committing murders and then disposing of the corpses. A fire of mysterious origin consumed the building on August 19, 1895, and the site is currently occupied by a U.S. Post Office building.
The number of his victims has typically been estimated between 20 and 100, and even as high as 200, based upon missing persons reports of the time as well as the testimony of Holmes's neighbors who reported seeing him accompany unidentified young women into his hotel—young women whom they never saw exit. The discrepancy in numbers can perhaps best be attributed to the fact that a great many people came to Chicago to see the World's Fair but, for one reason or another, never returned home. The only verified number is 27,although police had commented that some of the bodies in the basement were so badly dismembered and decomposed that it was difficult to tell how many bodies there actually were. Holmes' victims were primarily women (and primarily blond), but included some men and children.

Trial and execution

While Holmes sat in prison in Philadelphia, not only did the Chicago police investigate his operations in that city, but the Philadelphia police began to try to unravel the Pitezel situation—in particular, the fate of the three missing children. Philadelphia detective Frank Geyer was given the task of finding out. His quest for the children, like the search of Holmes's Castle, received wide publicity. His eventual discovery of their remains essentially sealed Holmes's fate, at least in the public mind.
Holmes was put on trial for the murder of Pitezel and confessed, following his conviction, to 27 murders in Chicago, Indianapolis and Toronto, and six attempted murders. Holmes was paid USD$7,500 ($197,340 in today's dollars) by the Hearst Newspapers in exchange for this confession. He gave various contradictory accounts of his life, claiming initially innocence and later that he was possessed by Satan. His faculty for lying has made it difficult for researchers to ascertain any truth on the basis of his statements.

On May 7, 1896, Holmes was hanged at Moyamensing Prison, also known as the Philadelphia County Prison. Until the moment of his death, Holmes remained calm and amiable, showing very few signs of fear, anxiety or depression. Holmes's neck did not snap immediately; he instead died slowly, twitching over 15 minutes before being pronounced dead 20 minutes after the trap had been sprung. He requested that he be buried in concrete so that no one could ever dig him up and dissect his body, as he had dissected so many others. This request was granted.

On New Year's Eve, 1909, Marion Hedgepeth, who had been pardoned for informing on Holmes, was shot and killed by Edward Jaburek, a police officer, during a holdup at a Chicago saloon. He was buried at the Cook County Cemetery on the grounds of the Cook County Poor Farm at Dunning. Then, on March 7, 1914, the Chicago Tribune reported that, with the death of the former caretaker of the Murder Castle, Pat Quinlan, "the mysteries of Holmes' Castle" would remain unexplained. Quinlan had committed suicide by taking strychnine.Quinlan's surviving relatives claimed Quinlan had been "haunted" for several months before his death and could not sleep.