Residents in the California community of Stockton have been living in fear of a possible serial killer that police believe is responsible for at least 5 recent murders.

In an interview with ABC News, the police chief of Stockton said the individual is on a "mission to kill" and before the murders, all the victims have been alone and the attacks occurred "at night or in the early morning."

It may shock you to know that at any given time, the FBI estimates there are between "25 and 50 active serial killers" in the United States at any given time, according to WorldAtlas.

Some of the more well-known serial killers in history are the Zodiac Killer, The Denver Prostitute Killer, and the Long Island Serial Killer.

Before any of these previously mentioned individuals became infamous, there was America's first serial killer who terrorized Chicago in the 1890s, more than 130 years ago.

His real name was Herman Mudgett from New Hampshire, and after moving to Chicago, took a job as a pharmacist and went under the name Doctor H.H. Holmes.

Soon after arriving in the Windy City in 1886, Holmes began killing people to steal their property, according to Britannica.

H.H. Holmes built a home in Chicago that had "secret passages, trapdoors, soundproof rooms, doors that could be locked from the outside, gas jets to asphyxiate victims, and a kiln to cremate the bodies," according to his biography in Britannica.

Before he was arrested in 1894 in Boston and ultimately sentenced to death by hanging, Holmes admitted to killing more than 130 people, but that number is believed to be closer to 200, according to researchers.

Some researchers have walked in Holmes' footsteps, searching for the locations where many of his grizzly killings took place around the city of Chicago.

LOOK: The states with the most UFO sightings

For each state, we’ve also included details of famous UFO sightings in that state. Of note is that almost three-quarters of all UFO sighting reports in the United States occur between 4 p.m. and midnight, and tend to peak between 9 and 10 p.m. Food for thought next time you're out scoping for alien life. Keep reading to see which states have had the most UFO sightings.

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