Everyone has heard the tagline "based on a true story" applied to horror movies, and it ramps up the excitement level and makes it more real. But what are the real stories behind these scary films? Check out these 12 movies based on well-known stories for the truth.

'Psycho' (1960) Paramount The Movie Story: Norman Bates is a psychologically disturbed hotel owner who has delusions this his dead mother, whose body he keeps in the cellar, wants to kill hotel guests. He develops a dual personality and dresses like her when he commits his murders. The Real Story: The character Norman Bates was inspired by Ed Gein, a Wisconsin man who was arrested in 1957 on charges of committing two murders and digging up the corpses of countless other women who reminded him of his dead mother. He skinned the bodies to make lampshades, socks, and a "woman suit" in hopes of becoming a woman. He was found to be insane and spent the rest of his life in a mental institution.

'The Sadist' (1963) Fairway International The Movie Story: Three teachers on their way to a baseball game in Los Angeles pull into a junkyard when their car malfunctions and end up being held at gunpoint by a young man named Charlie who demands they fix their car and then give it to him and his girlfriend. As the duo, who've killed several people in the past few days, waits, Charlie torments the captives verbally and physically. The Real Story: "Charlie" is based on Charles Starkweather, a 19-year-old who went on a notorious killing spree in 1957-58, murdering 11 people in Nebraska and Wyoming with his 14-year-old girlfriend, Caril Ann Fugate, in tow. Starkweather was arrested in 1958 and put to death in the electric chair in 1959. Fugate received a life sentence but was paroled after 17 years. Their exploits also inspired Oliver Stone's "Natural Born Killers" (1994) and Terrence Malick's "Badlands" (1973).

'The Exorcist' (1973) Warner Bros. The Movie Story: Two priests attempt to exorcize a demon that has possessed a 12-year-old girl living in the Georgetown neighborhood of Washington. The Real Story: William Peter Blatty, screenwriter, and author of the novel ​"The Exorcist," was inspired by an article he read in college at Georgetown University about an exorcism performed on a 13-year-old boy in Mount Rainier, Maryland, in 1949. The story's details have been muddled through the years—perhaps intentionally so, to protect the family—but the boy's actual home was in Cottage City, Maryland, and the exorcism was performed in St. Louis. Evidence points to the boy's behavior not being nearly as outrageous or supernatural as was portrayed in the film.

'The Texas Chainsaw Massacre' (1974) Bryanston Pictures The Movie Story: A group of young people traveling through rural Texas fall prey to a family of cannibals, including Leatherface, who wears a mask made from the skin of his victims. The Real Story: Again inspired by Ed Gein (see ​"Psycho"), whose exploits also inspired the films "Deranged" (1974) and, in part, ​"The Silence of the Lambs" (1991).

'Jaws' (1975) Universal The Movie Story: A 25-foot-long great white shark terrorizes the fictional Northeastern fishing community of Amity Island, attacking swimmers and boaters for several days during the summer. The Real Story: Screenwriter and novelist Peter Benchley was inspired in part by a series of shark attacks that plagued the New Jersey shore in 1916. Over a 12-day period in July of that year, five people were attacked, four of whom died. A 7-foot-long great white shark was killed on July 14, and its stomach was found to contain human remains. To this day, there is a debate over whether that shark was the culprit—some scientists argue that it was probably a bull shark—but no further attacks were reported that summer after it was killed.

'The Hills Have Eyes' (1977) Vanguard The Movie Story: A family driving through the Southwestern desert in an RV takes a shortcut that leads them to run headlong into a family of violent cannibals who live in caves in the hills. The Real Story: The movie was inspired by the legend of Alexander "Sawney" Bean, a Scotsman of the 15th or 16th century who reportedly headed a 40-person clan that killed and ate more than 1,000 people and lived in caves for 25 years before being caught and put to death. His life has inspired numerous stories, and films worldwide, including "The Hills Have Eyes" and the British film "Raw Meat" (1972), but most serious historians today don't believe that Bean ever existed.

'The Amityville Horror' (1979) American International Pictures The Movie Story: The Lutz family moves into a riverside house, the site of a mass murder the year before. They encounter a series of malevolent paranormal events that drive them out of the house after only 28 days. The Real Story: Perhaps the most notorious horror movie "based on a true story," the film is taken from a self-proclaimed nonfiction book describing what George and Kathy Lutz experienced during their four weeks in the house, including disembodied voices, cold spots, demonic imagery, inverted crucifixes, and walls "bleeding" green slime (not blood, as in the film). Most, if not all, of the events portrayed in both the book and the movie, have been called into question by investigators, and it is widely believed that the entire incident was a hoax.

'Gothic' (1986) Lionsgate The Movie Story: In 1816, poet Lord Byron gathers fellow poet Percy Bysshe Shelley and his soon-to-be-wife, Mary, along with Mary's half-sister Claire and Byron's doctor, John Polidori, at his Swiss mansion. They tell ghost stories and experience surreal supernatural encounters that are physical manifestations of their fears. The Real Story: In the rainy summer of 1816, Shelley and Mary Godwin (soon to be Shelley) visited Lord Byron at his Swiss villa. Because of the rain, they stayed indoors discussing the animation of dead matter and reading German ghost stories. Byron suggested they each write their own supernatural tale, and Godwin came up with "Frankenstein," while Byron wrote what would later be adapted by Polidori into "The Vampyre."

'Henry: Portrait of a Serial Killer' (1986) Dark Sky The Movie Story: Henry is a serial killer who's killed hundreds of people, sometimes aided by his roommate, Otis. He finds some solace in Otis's sister, Becky. The Real Story: Writer/director John McNaughton was inspired by serial killer Henry Lee Lucas, who had an accomplice named Ottis Toole and a romantic relationship with Otis' young relative (his niece, Frieda Powell). However, the movie's killing spree is based more on Lucas' confessions than on fact. Lucas confessed to 600 murders, in part because the confessions led police to offer him improved conditions in jail. Most of his confessions were disproved, but Lucas was still convicted of 11 murders, including Powell's, and spent the rest of his life in prison.

'An American Haunting' (2006) Freestyle The Movie Story: Nineteenth-century landowner John Bell and his family are tormented by an invisible entity, which targets his daughter Betsy in particular. The Real Story: The movie is based on the legend of the Bell Witch, a tale that originated in Tennessee in the 1800s. It is believed by many to be a work of fiction, although the characters in the story were real. According to the tale, John Bell was poisoned by the ghost, and although the film's marketing declared that it is "validated by the State of Tennessee as the only case in U.S. history where a spirit has caused the death of a human being," there is no such validation on record. Some claim that "The Blair Witch Project" (1999) was also influenced by the story.

'The Sacrament' (2014) Magnet Releasing The Movie Story: A photographer is permitted to visit his sister, who lives in a secretive, cult-like commune named Eden Parish headed by the mysterious "Father." He brings along his journalist co-workers Sam and Jake to document the journey for a possible news story, but they bite off more than they can chew when the dark underbelly of the seemingly idyllic community is exposed. The Real Story: The infamous Jonestown Massacre occurred in November 1978 in the jungles of Guyana in a commune headed by Jim Jones. As in the movie, the beginning of the end started when a TV crew—this one accompanying U.S. Rep. Leo Ryan, who was investigating reports of mistreatment of commune members—visited, and someone slipped them a note asking for help. Ryan and the TV crew agreed to take anyone who wanted to leave back to the U.S., but as they waited for the plane on the tarmac, members of the commune opened fire, killing Ryan and four others. Back at Jonestown, Jones instructed his followers to kill themselves by drinking poisoned Flavor Aid, which 918 people did. Jones himself died from a gunshot to the head, although it's unclear if he pulled the trigger.