Oct. 4 (UPI) — In 1982, cyanide-laced Tylenol capsules killed seven people in the Chicago area, sparking one of the first massive recalls in the United States and revolutionizing packaging for over-the-counter medications sold in the country. But the case has never been solved.

The deaths began on Sept. 29, when 12-year-old Mary Kellerman died within hours of taken a capsule of Extra-Strength Tylenol. Later that same day, a postal worker, Adam Janus died. Both had been poisoned with potassium cyanide, which investigators later determined had been put inside the capsules of Tylenol.

Another five people would die, including Adam Janus’ brother, Stanley Janus and sister-in-law Theresa Janus, who had taken capsules from the same bottle of Tylenol that killed the postal worker. Mary McFarland, Paula Prince and Mary Reiner, all living in or near Chicago, also died. Tylenol samples taken from each of the victims’ homes tested positive for cyanide.

The results of the test prompted one of the first massive recalls in U.S. history. Thirty-five years ago today, on Oct. 5, 1982, Johnson & Johnson, the maker of Tylenol, pulled millions of dollars worth of product off store shelves, reducing the company’s earnings by $50 million. There was nationwide panic as worried consumers went to hospitals out of fear of poisoning. The Food and Drug Administration counted hundreds of copycat incidents nationwide, including one in 1986 in which two people in died after taking cyanide-laced Excedrin capsules.

Investigators believe someone pulled packages of the capsules off the shelf, opened up the capsules and replaced the drug inside with cyanide before putting the packages back on the shelf. The ease with which capsules can be contaminated prompted drugmakers to move away from capsules and instead produce solid caplets. Companies also began implementing the use of tamper-resistant packaging for the drugs.

Despite the far-reaching impact of the case, the FBI never solved the question of who was responsible for the tampering.

The only person convicted in relation to the case was James Lewis, who sent a letter to Johnson & Johnson demanding $1 million in order to “stop the killings.” He spent 12 years in prison for extortion, but police never charged him with tampering with the capsules.

In 2011, the FBI investigated the possibility so-called “Unabomber” Theodore Kaczynski, who grew up in the Chicago area, may have been behind the killings.

The Chicago Daily Herald said the FBI handed over the case to the Arlington Heights, Ill., Police Department. Deputy Chief Mike Hernandez told the newspaper the department is concerned too much time has passed in order to solve the crime.

“We’re concerned about how long it’s been. It’s been a concern of the task force, as more time goes by,” he said.

Years after the initial deaths, advances in technology allowed investigators to potential DNA evidence and a fingerprint smudge on one of the Tylenol bottles. But neither resulted in any arrests.

Though investigators on the case no longer regularly meet, the Daily Herald said, Hernandez said there’s still hope.

“But this case is still a high priority. It’s not gathering dust,” he said.