(CNN) It started with a series of mysterious deaths in the Chicago area on September 29, 1982: a 12-year-old in Elk Grove Village, a postal worker in Arlington Heights, a new mother of four in Winfield.

Inexplicably, they fell ill and were pronounced dead.

"We didn't know what was happening, but everybody thought he died of heart attack," said Joseph Janus, brother of postal worker Adam Janus.

But after relatives arrived to console their grieving family, another of Adam's brothers, Stanley Janus, grabbed his chest and fell to the ground.

"Foam is coming out of his mouth," Joseph said. "His eyes were upside down."

For the second time that day, an ambulance pulled up to the Janus house. And then, another family member collapsed: Stanley's wife, Theresa.

Authorities quarantined the house and, suspecting a health issue, called the village nurse to look for clues. And she found one: The victims had taken Tylenol. In the trash, she found a receipt for a bottle that had been purchased that morning.

"It's got to be the Tylenol," former Arlington Heights village nurse Helen Jensen recalled thinking. "Something's wrong with the Tylenol."

The 'Tylenol murders'

They came to be known as the "Tylenol murders": seven people, three of them from the Janus family, who died from what investigators discovered were cyanide-laced Tylenol capsules.

Cyanide is a poison that blocks the body's ability to use oxygen, according to the US Centers for Disease Control and Prevention. It's particularly harmful to the heart and brain because those organs use a lot of oxygen, the agency says.

"It works very fast. No question about it," said Dr. Edmund Donoghue, who worked on the case as Cook County's deputy chief medical examiner.

In its solid crystal form, cyanide can be lethal to humans in quantities far less than a gram, though people have survived after ingesting more than that.

One giveaway that cyanide was behind the murders was how the bottle smelled.

"Classically, the smell of cyanide is described as ... bitter almonds," said Donoghue, who asked one investigator over the phone to take a whiff. "Some people would just say it's a very pungent odor."

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Once investigators discovered that someone had put cyanide in the capsules, consumers were warned not to take the drug, and 31 million bottles nationwide were recalled by manufacturer Johnson & Johnson. The company cooperated with investigators and later offered a $100,000 reward for information that might identify and convict whoever was to blame.

The drug company ended up testing 1.5 million bottles and finding three unopened bottles contaminated with cyanide -- bringing the total to 10 bottles that had been tampered with.

"If you took this medicine and there was cyanide in it, you were going to die," Donoghue said.

More than three decades later, the case remains unsolved.

The complete package

Officials never identified the killer, but they did try to prevent it from happening again.

That year, the US Food and Drug Administration issued its first regulations for tamper-resistant packaging of over-the-counter drugs. Johnson & Johnson unveiled plans for triple-sealed Tylenol packaging: a box with glued flaps, a plastic ring around the neck and a foil seal that's now commonplace among over-the-counter drugs.

Johnson and Johnson later pushed solid "caplets" instead of powder-filled capsules, the kind that had been filled with cyanide. Congress also passed a bill in 1983 that made it a federal crime to tamper with medications and other consumer goods.

The makers of Tylenol and other drugs have updated packaging to counter tampering since the 1980s, when the bottle on the left was made. The bottle on right is from the mid-2000s.

The FDA's over-the-counter packaging requirements call for drug makers to say on the label how you'll know whether someone's opened it before you. These "tamper-evident" features may involve the use of logos, breakable seals, blister packs or tape.

These changes didn't just give consumers a tool to identify drugs that had been opened or adulterated; they changed the way we think about the products we purchase and what they should look like, according to Jay Kennedy , an assistant professor in the School of Criminal Justice and the Center for Anti-Counterfeiting and Product Protection at Michigan State University.

"It shifted our perception of the packaging, but it also raised our awareness and made us conscious of the risks that exist," Kennedy said.

After reports of Tylenol tampering in 1986, the pain reliever was removed from the shelves of some drugstores.

But 1982 wasn't the end of it: A number of copycats followed, including cyanide-tainted Tylenol that claimed a victim in New York in 1986; a woman who laced Excedrin with cyanide, killing her husband and a stranger in 1986; and a Seattle man who put cyanide into Sudafed in 1991 in an attempt to kill his wife, killing two strangers instead.

"The risk always exists," Kennedy said. But with current packaging, "it would be very expensive, very labor-intensive. It'd be difficult to get these things in and out of the system."

A more prevalent concern, he said, is counterfeit drugs made by those whose main goal is to make money and fly under the radar, not to kill people. These products may be sold through online pharmacies or sneaked into the legitimate supply chain.

To combat that and comport with recent drug security policies , manufacturers have developed technological ways to design and identify their products. Many of them are "covert features," unknown to consumers but used by professionals to tell when something is amiss, Kennedy added.

But to prevent what happened decades ago in Chicago, the layers of plastic, seals and foil "have stood the test of time," though there are no publicly available data on how often they save consumers from danger, he said.

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Monica Janus, who was in the house when her two uncles and aunt fell victim in 1982, sees this as a silver lining to what happened that day.

"I see them looking down at all of us," she said. "I know they're here thinking this was a positive for the world.

"Everywhere that you go, when you go to a store, everything is sealed. And the seals are to protect the human race from people tampering with products.

"Maybe this was supposed to happen -- to save other people's lives."