Who is believed to be America's first serial killer?

Herman Webster Mudgett (May 16, 1861 – May 7, 1896), better known under the name of Dr. Henry Howard Holmes or more commonly H. H. Holmes, was American's first serial killer. He was identified by the Chicago police as a serial killer

While he confessed to 27 murders, only nine could be plausibly confirmed and several of the people whom he claimed to have murdered were still alive. He is commonly said to have killed as many as 200, though this figure is traceable only to 1940's pulp magazines. Many victims were said to have been killed in a mixed-use building he owned, located about 3 miles (4.8 km) west of the1893 World's Fair: Columbian Exposition in Chicago, supposedly called World's Fair Hotel (informally "The Murder Hotel"), though evidence suggests that the hotel portion was never truly open for business.

Besides being a serial killer, Holmes was also a con artist and a bigamist, the subject of more than 50 lawsuits in Chicago alone. Many now-common stories of his crimes sprang from fictional accounts that later authors took for fact in a 2017 biography, Adam Selzer wrote that Holmes' story is "effectively a new American tall tale.

H. H. Holmes was executed on May 7, 1896, for the murder of friend and accomplice Benjamin Pitezel. During his murder trial for Pitezel, H. H. Holmes confessed to numerous other killings. Although never proven many Ripper experts believe he was Jack The Ripper as his killings were done in the same style as The Ripper.