Tylenol murders: Cause of death revealed for sole suspect in 1982 poisonings

The cause of death for the sole suspect in the 1982 Tylenol poisonings that killed seven people in the Chicago area has been revealed.

James Lewis was found dead last month in his Cambridge, Massachusetts, home. He was 76 years old.

On Thursday, the Massachusetts Office of the Chief Medical Examiner said Lewis died of a pulmonary embolism. His death was from natural causes. 

This comes 40 years after seven people were poisoned and killed by swallowing tablets laced with a lethal dose of cyanide.

Lewis had inserted himself into the investigation by sending an extortion letter to the drug's manufacturer, but he always maintained his innocence. Authorities determined that Lewis wasn't in the Chicago area at the time.

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When he was arrested in 1982 after a nationwide manhunt, he gave investigators a detailed account of how the killer might have operated.

He was convicted of extortion and served 13 years in prison. Some investigators still believe Lewis was behind the murders, which he has repeatedly denied.

Investigators had been interviewing Lewis as recently as September as part of a renewed effort to bring charges in the case but now with the only suspect dead, it is unlikely that will ever happen.

The Associated Press contributed to this report.