James W. Lewis, Suspect in the 1982 Tylenol Murders, Dies at 76

James W. Lewis, the prime suspect in the deaths of seven people in 1982 from cyanide-laced Tylenol, a poisoning that terrified the nation and changed the way manufacturers packaged medications, died on Sunday in Cambridge, Mass. He was 76.

Mr. Lewis was pronounced dead after the authorities responded to a report of an unresponsive person at his home, Superintendent Frederick Cabral of the Cambridge Police Department said on Monday. The cause of death was “not suspicious,” Superintendent Cabral said, declining to comment further.

Mr. Lewis spent more than four decades under scrutiny in connection with the notorious unsolved poisonings, in which someone laced Extra-Strength Tylenol with deadly potassium cyanide, killing seven people in the Chicago area in September and October of 1982.

Mr. Lewis was never charged in the murders, and he denied any involvement in them. But in October 1982, he sent a letter to Johnson & Johnson, the parent company of MacNeil Consumer Products, the manufacturer of Tylenol, saying he would “stop the killing” if he were paid $1 million. He was convicted of extortion in 1983 and spent 12 years in federal prison.

After Mr. Lewis was convicted, he offered prosecutors help in solving the Tylenol murders.

“He is a prolific writer and artist,” Jeremy Margolis, a former federal prosecutor in Chicago who handled the extortion case against Mr. Lewis, told The New York Times in 2009, “and he provided me with great volumes of documents and a number of diagrams, all of which dealt with his theories as to what might have taken place.”

But Mr. Lewis steadfastly denied any involvement in the killings. When he was a fugitive on the extortion charge, he wrote a series of rambling letters to The Chicago Tribune disclaiming any connection to the murders. In one, he called himself “a victim,” and demanded capital punishment for “whoever poisoned those capsules.”

Mr. Lewis was born on Aug. 8, 1946. He was variously described in news reports as a tax consultant and tax accountant.

In 1978, he was charged with murder in the death of Raymond West, a 72-year-old man from Kansas City, Mo., who had hired him as an accountant.

Mr. West’s dismembered and decomposed body was found hanging from a pulley in his attic the same day Mr. Lewis tried to cash a forged check on Mr. West’s account. The case was dismissed after the judge found that the police did not inform Mr. Lewis of his rights at the time of his arrest.

In 1983, Mr. Lewis was convicted on six counts of mail fraud in connection with a scheme to obtain credit cards by using information from clients of his tax preparation service in Kansas City in 1981.

In 1995, after he was released from prison in the Tylenol extortion case, Mr. Lewis moved to the Boston area.

He was indicted in Massachusetts in 2004 on charges of aggravated rape, drugging a person with “intent to stupefy or overpower” for sexual intercourse, and four other charges, The Boston Globe reported. He was held without bail until 2007, when the victim declined to go forward with the prosecution, The Globe reported.

Over the years, investigators continued to scrutinize Mr. Lewis in connection with the Tylenol murders.

In 2009, F.B.I. agents executed a search warrant at the condominium complex in Cambridge where he lived. In 2010, Mr. Lewis attracted fresh attention when he released a self-published novel, “Poison!: The Doctor’s Dilemma.” And just last year, on the 40th anniversary of the killings, investigators traveled from Illinois to interview Mr. Lewis as they continued to try to crack the case, the local CBS affiliate in Chicago reported.

The deaths, including that of a 12-year-old girl who had swallowed a Tylenol capsule hoping to fend off a cold, spread terror throughout the country and made Americans wonder if they could trust familiar products on grocery and pharmacy shelves.

Drugstores and supermarkets across the United States removed Tylenol from their shelves. State and local health officials issued warnings, and thousands of worried people who had taken the popular pain reliever flooded hospitals, doctors’ offices and poison-control centers with calls.

In response to the deaths, Johnson & Johnson ordered a nationwide recall of 31 million bottles of Tylenol, with a retail value of more than $100 million. The company pulled its television commercials off the air. And it offered $100,000 for information leading to the arrest and conviction of the “person or persons responsible for the murders.”

Just six weeks after the crisis erupted, the company also offered a solution: a new Tylenol bottle with safety features to prevent tampering including a cotton wad, foil seal, childproof cap and plastic strip. The design is now widely used throughout the industry. Capsules began to be replaced with caplets the following year.

The search for the culprit, however, proved elusive.

After the deaths, more than 100 state and federal agents fanned out across the Chicago area in an effort to reconstruct the route of the poisoned capsules. But they could not determine the source. Melaney Arnold, a spokeswoman for the Illinois State Police, said in a statement on Monday that, “at this time, the investigation is still ongoing.”