There are still a number of American serial killers who have never been caught after committing multiple murders in a gruesome fashion over the past years.

The stories of these uncaught serial killers keep the public up at night or make a person double-check their front door lock. It is disturbing to read and know about the atrocious acts committed by these serial murderers.

Notorious American Serial Killers Who May Still Be Out There

The following list explores the horrifying accounts of some of the most notorious American serial killers still at large.

The Zodiac Killer

The Zodiac Killer is likely the most infamous unsolved serial killer case in the U.S., largely due to Jake Gyllenhaal and Robert Downey, Jr.'s 2007 film, "Zodiac." The Zodiac Killer reportedly committed his horrific crimes in Northern California in the late 1960s.

He was linked to five murders from 1968 to 1969 and might have been responsible for more, as he claimed to have killed 37 people. 

According to How Stuff Works, the Zodiac Killer made himself known to city residents by leaving clues at the crime scenes, threatening to shoot school buses filled with kids, and sending pieces of his victims' clothes to the San Francisco Chronicle newspaper.

His trademark was taunting police by sending letters to local newspapers. He also threatened the public if the newspapers would not publish his cryptic letters.

The first murder crime attributed to the Zodiac Killer happened on the night of December 20, 1968, when David Faraday, 17, and his girlfriend, Betty Lou Jensen, 16, were shot to death near their car on Lake Herman Road in Benicia, California.

To this day, no one has been arrested for these murders. There have been numerous suspects in the past years, but the case is still open. The identity of the Zodiac Killer has also remained unknown.

The Doodler

Earlier this year, investigators thought they were getting closer to solving one of San Francisco's most notorious cold case murders. Throughout the 1970s, a serial killer, only known as "The Doodler," terrorized gay men without ever being caught.

Investigators said he had visited gay clubs in the Castro and Polk Gulch, including the Cinch Saloon, which is still open today and was allegedly one of The Doodler's "hunting grounds" in the 1970s.

He reportedly sexually assaulted and stabbed his victims, ultimately murdering between six and 14 victims in San Francisco. Reports said the serial killer usually picked a guy at a bar, sat at the table, and sketched them. He would then walk up to the guy and say, "Like my doodle?"

One of his victims was Joseph "Jae Stevens," 27, who was found brutally stabbed at Spreckels Lake in Golden Gate Park in 1974.

According to ABC News, the San Francisco police already have two sketches of the man they believe is The Doodler, and they also doubled the reward to $200,000 to help them find the suspect. However, no one has been arrested up to this day.

The West Mesa Bone Collector

It is possible that the so-called West Mesa Bone Collector, one of the terrifying American serial killers, is still at large in Albuquerque or somewhere in New Mexico.

In 2009, the public learned about the unidentified killer when authorities unearthed 11 skeletons in the Albuquerque suburb of West Mesa. After receiving information that a woman saw a human femur bone partially exposed in a vacant building site, police excavated the area.

Two women reported missing in 2003 and 2005 were found dead in that location. However, reports said the West Mesa Bone Collector may have also been responsible for the disappearance of 13 other women reported missing as recently as 2006.

Although police considered several suspects, they did not have enough evidence to make a strong case against anyone.

The Alphabet Killer

The Alphabet Killer committed his crimes in Rochester, New York, during the early 1970s and was one of the most interesting American serial killers.

The murderer chose to kill young women whose first and last names started with the same letter, hence his moniker. Authorities said the Alphabet Killer's three victims, aged 10 to 11, were raped and strangled between 1971 and 1973. 

Even though there were numerous witnesses, including multiple drivers who saw 10-year-old Carmen Colon half-naked on the side of the road trying to flee the attacker, police could not solve the case.

Law enforcement officers maintained tabs on several persons, including one who had ties to the investigation as recently as 2011. However, none of the four men considered by police could be linked to these crimes, though one was sentenced to death for the sex workers' murders in Nevada.

The Long Island Killer

In 1996, police discovered human remains near Gilgo Beach on Long Island's South Shore, and over the next decade, they made numerous further discoveries. But it was in 2010 that investigators considered the possibility that the Long Island Killer was responsible for all of the murders, according to ATI.

That year, police found the remains of four bodies while searching for Shannan Gilbert, who had gone missing seven months earlier. By the end of 2011, six more human remains were reportedly found near the same stretch of Ocean Parkway and Gilgo Beach.

The Long Island Killer allegedly committed  between 10 and 17 murders. The American serial killer has remained mysterious for over two decades.

Even after years of investigation and countless leads, the case goes cold repeatedly. The Long Island Killer is one of the most recent serial killers in America to remain at large.

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Written by: Bert Hoover

Watch: The Horrifying Murders Of The Zodiac Killer - From BuzzFeed Unsolved Network