A bottle of pain reliever. A familiar brand. A normal morning.

In late September 1982, seven people across the Chicago area took Extra-Strength Tylenol capsules for everyday reasons.

But within days, all seven were dead.

The capsules had been contaminated with potassium cyanide.

Mary Kellerman was 12 years old. Adam Janus was 27. Adam’s brother, Stanley Janus, and Stanley’s wife, Theresa, both took capsules from the same bottle and became victims, too. Mary McFarland, Lynn Reiner, and Paula Prince were also killed.

Investigators ultimately recovered eight cyanide-tainted bottles and identified 56 contaminated capsules. The evidence pointed to tampering after the product had left the manufacturer and entered the retail system—but the person, or people, responsible have never been identified.

In this episode of M ...