Wednesday, September 29, 1982 was a school day, but 12-year-old Mary Kellerman woke up with a runny nose and a headache. So her parents told her to stay home, take a couple of Tylenol and get some rest.

“I heard her go into the bathroom. I heard the door close. Then I heard something drop,” recalled Dennis Kellerman, Mary’s dad. “I went to the bathroom door. I called, ‘Mary, are you OK?’ There was no answer. I called again: ‘Mary, are you OK?’ There was still no answer. So I opened the bathroom door, and my little girl was on the floor unconscious. She was still in her pajamas.”

Mary was pronounced dead at the hospital from unknown causes.

A few hours later, in a nearby suburb of Chicago, a 27-year-old postal worker named Adam Janus had also taken a sick day. After lunch, he complained to his wife about a headache and took two Extra-Strength Tylenol. Like Mary, Adam collapsed on the floor almost instantly and couldn’t be resuscitated. The paramedics ruled it a massive heart attack.

Adam Janus’s relatives rushed to the house to console his grieving wife. Overcome by Adam’s sudden passing, his younger brother and sister-in-law asked for some Tylenol. They were the next to die.

All told, seven people in the Chicago area died suddenly and mysteriously on September 29 and 30, 1982. One was a mother of four, including a week-old infant. Another, a healthy, 31-year-old, crumpled to the floor at work. The last victim, a flight attendant, was found dead in her apartment three days later, an open bottle of Tylenol still on the bathroom counter.

Investigators and toxicologists quickly identified the culprit: tampered capsules of Extra-Strength Tylenol. Someone had opened the capsules and replaced the pain-relieving medicine with deadly doses of potassium cyanide. One of the most common over-the-counter pain relievers had been turned into a murder weapon.

The 1982 Tylenol murders rocked the nation. The seven deaths were the top story in every major newspaper on October 1, the official start of the Halloween season, and the “Tylenol Terrorist,” as the media dubbed him, was still on the loose.

For decades, Americans had been told scary tales of Halloween treats supposedly spiked with razor blades and rat poison, but the Tylenol murders ratcheted up the anxiety around treat-or-treating to new levels, prompting cities and towns across the country to cancel Halloween.

The official response to the Tylenol murders was swift.

The manufacturer of Tylenol, a subsidiary of Johnson & Johnson called McNeil Consumer Products, initiated the largest consumer product recall in American history, ordering pharmacies and grocery stores to pull 31 million bottles of Extra-Strength Tylenol from their shelves. Several more bottles in the Chicago area were found to contain cyanide, but thankfully no one else was hurt.

The federal government also swept into action. Congress passed the Federal Anti-Tampering Act, which promised up to 20 years in jail for anyone found tampering with medications, food or other consumer goods. And the Food and Drug Administration (FDA) passed new regulations requiring drugmakers to package medications like Tylenol in new, tamper-proof bottles. (“Child-resistant” caps had been around since 1970.)

“[The 1982 Tylenol poisonings] was one of those pivotal moments,” says Dr. Alan Woolf, a pediatrician at Boston Children’s Hospital and a professor of pediatrics at Harvard Medical School. “Forty years later, we take it for granted that bottles of over-the-counter medicine are shrink-wrapped in plastic and there’s a piece of foil that you need to peel back. Those tragic killings changed the pharmaceutical industry and changed federal labeling laws.”

The public’s response to the Tylenol murders was “abject fear,” says Woolf, whose book, History of Modern Toxicology, includes a chapter on the 1982 poisonings.

And since the murders happened so close to Halloween, people immediately transferred their anxiety about tainted over-the-counter drugs to longstanding fears about tainted Halloween candy.

Joel Best is the leading expert on “Halloween sadism,” the alleged practice of giving contaminated treats to children on Halloween. A professor of sociology and criminal justice at the University of Delaware, Best has traced the emergence of this “contemporary legend” back to the beginning of organized trick-or-treating in the 1950s.

“Almost immediately there are stories of people heating pennies in a skillet and dumping the red-hot coins into the outstretched hands of trick-or-treaters,” says Best.

Reports of Halloween sadism really took off in the late 1960s and early 1970s when the public’s anxieties ran deep over the Vietnam War, the counterculture movement, and new terms like “child abuse.”

In 1970, The New York Times ran a story warning about razor blades in apples, chocolate bars replaced with laxatives and candy packets containing sleeping pills. The article quoted the New York State Health Commissioner, who claimed that pins, razor blades, broken glass and poison had all been found in Halloween candy.

When asked why someone would poison a child’s Halloween candy, a psychiatrist named Dr. Reginald Steen blamed “the permissiveness in today's society,” which resulted in “people getting away with more and more violence. The people who give harmful treats to children see criminals and students in campus riots getting away with things, so they think they can get away with it, too.”

In 1985, Best published a research paper that investigated all known claims of Halloween sadism since 1958 and came to a surprising conclusion. In Best’s words, he was “unable to find a substantiated report of a child being killed or seriously injured by a contaminated treat picked up in the course of trick-or-treating.”

Every report of a razor blade or pin or ant poison found in Halloween candy turned out to be a hoax perpetrated by kids or adults. And the few tragic cases where a child died on or around Halloween, and were widely attributed to tainted candy, were confirmed by medical records to be the result of heart defects, infections and other explainable illnesses.

The only confirmed report of a child being poisoned and killed by a piece of Halloween candy was the unfortunate case of Timothy O'Bryan, an 8-year-old from Texas who died after eating Halloween candy laced with cyanide. The murderer wasn’t a creepy neighbor, but sadly Timothy’s own father, who killed the boy in order to cash in on an insurance policy. The father was convicted and given the death penalty.

“When the Tylenol story broke at the beginning of October, people almost instantly started relating the poisonings to the dangers of kids going trick-or-treating and being given contaminated stuff,” says Best.

The Halloween fears were the strongest in Chicago, where the community was still reeling from the murders and no arrests had been made. Bob Greene, a columnist for the Chicago Tribune, wrote: "If you are a parent, and you have any sense, you will forbid your child from going out trick-or-treating this Halloween… in this year of the Tylenol killer it would be especially foolish to let a boy or girl go door-to-door asking for food."

The mayor of Chicago distributed 1 million leaflets encouraging Chicagoans to hand out money or small toys instead of candy on Halloween. In a suburban Chicago subdivision called Poplar Hills, the homeowners association asked residents to hand out coupons for candy that could be redeemed at nearby stores.

But also far from Chicago, communities like Vineland, New Jersey canceled trick-or-treating altogether, and other suburbs and small towns followed suit in Ohio, Pennsylvania and Massachusetts.

According to Best, who tracks reports of Halloween sadism going back to 1958, there were 12 reported cases of Halloween candy contamination in 1982, second only to 1971, when there were 14 such reports. As Best is quick to emphasize, though, a “report” of Halloween sadism is not the same as an actual occurrence.

Despite a 40-year ongoing investigation by the FBI and other law enforcement, the perpetrator of the Tylenol murders has never been found.