Tylenol has been for decades the best-selling, non-prescription pain reliever in the United States. It used to come as gelatin capsules, pills that were possible to open, and that meant anyone could remove its active ingredient, acetaminophen, and replace the contents with ... anything else. And someone did, resulting in the deaths of seven people by cyanide poisoning. Holly and Maria look at how the case unfolded, and how more than 40 years later, the identity of the person who tampered with Tylenol is still unknown.