By the time of his execution in 1896, Holmes had engaged in a lengthy criminal career that included insurance fraud, forgery, swindling, three or four bigamous marriages, horse theft, and murder.

[3] Much of the lore attached to Holmes concerns the so-called "Murder Castle", a three-story building he commissioned on W. 63rd Street in Chicago, Illinois.

Details about the building, along with many of his alleged crimes, are considered exaggerated or fabricated for sensationalistic tabloid pieces with some accounts estimating his body count could be as high as 133[4] or even 200.

Many of these inaccuracies have persisted due to the combination of ineffective police investigation and hyperbolic yellow journalism of the period, which are often cited as historical record.

In his book about Holmes, author Adam Selzer writes: "Just killing several people isn't necessarily enough for most definitions [of a serial killer].

More often, it has to be a series of similar crimes, committed over a period of time, usually more to satisfy a psychological urge on the killer's part than any more practical motive."

[18] Soon after his arrival, he came across a drugstore at the northwest corner of South Wallace Avenue and West 63rd Street in the Englewood section of Chicago.

[19] The drugstore's owner, Elizabeth Holton, gave Holmes a job; he proved to be a hardworking employee, eventually buying the store.

[21] Holmes purchased an empty lot across the street, where construction began in 1887 for a two-story mixed-use building, with apartments on the second floor and retail spaces, including a new drugstore, on the first.

[22] Contemporary accounts report that Holmes built the hotel to lure tourists visiting the Exposition in order to kill them and sell their skeletons to nearby medical schools.

In reality, the third-floor hotel was moderately sized, largely unremarkable and uncompleted due to Holmes's disputes with the builders.

[24] In his confession, Holmes stated that his usual method of killing was to suffocate his victims using various means, including an overdose of chloroform, overexposure to lighting gas fumes, and trapping them in an airless vault.

[25] Holmes's hotel was gutted by a fire started by an unknown arsonist shortly after his arrest, but was largely rebuilt and used as a post office until 1938.

[40] In July 1894, Holmes was arrested and briefly jailed for the first time, on the charge of selling mortgaged goods in St. Louis, Missouri.

[41] He was promptly bailed out, but while in jail he struck up a conversation with a convicted outlaw named Marion Hedgepeth, who was serving a 25-year sentence.

[6] Pitezel agreed to fake his own death so that his wife could collect on a $10,000 life insurance policy,[6] which he was to split with Holmes and Howe.

The scheme, which was to take place in Philadelphia, called for Pitezel to set himself up as an inventor under the name "B.F. Perry", and then be killed and disfigured in a lab explosion.

Holmes then went on to manipulate Pitezel's unsuspecting wife, Carrie Alice Canning, into allowing three of her five children to be placed in his custody.

[6][44] Frank Geyer was a Philadelphia Police Department detective assigned to investigate Holmes and find the three missing children.

Geyer began in June 1894 to trace Holmes's steps, and found the decomposed bodies of the two Pitezel girls in the cellar of the Toronto home.

[45] The detective wrote: "The deeper we dug, the more horrible the odor became, and when we reached the depth of three feet, we discovered what appeared to be the bone of the forearm of a human being.

[46] Holmes was reported to have visited a local pharmacy to purchase the drugs which he had used to kill Howard Pitezel on October 10, 1894, and a repair shop to sharpen the knives he used to chop up the body before he burned it.

[6][47] Holmes's murder spree finally ended when he was arrested in Boston on November 17, 1894, after being tracked there from Philadelphia by the private Pinkerton National Detective Agency.

He was held on an outstanding warrant for horse theft in Texas because the authorities had become more suspicious at this point and Holmes appeared poised to flee the country in the company of his unsuspecting third wife.

[6][48] In July 1895, following the discovery of Alice and Nellie's bodies, Chicago police and reporters began investigating Holmes's building in Englewood, now locally referred to as the "Castle".

[6][9] as there was only very circumstantial physical evidence of the "Castle" victims: a piece of human bone possibly from Julia Conner; remains of a child, possibly Pearl Conner; a burned gold watch chain and burned dress buttons-apparently belonging to Minnie Williams; and a tuft of human female hair found in a chimney flue.

[1][56] Until the moment of his death, Holmes remained calm and amiable, showing very few signs of fear, anxiety, or depression.

[57] Despite this, he asked for his coffin to be contained in concrete and buried ten feet deep, because he was concerned grave robbers would steal his body and use it for dissection.

On New Year's Eve 1909, Hedgepeth, who had been pardoned for informing on Holmes,[1] was shot and killed by Police Officer Edward Jaburek during a hold-up at a Chicago bar.

Before moving to Chicago, he changed his name to "Henry Howard Holmes" to avoid the possibility of being exposed by victims of his previous scams.