Investigators raced to find out who committed these random crimes and why. But there was something in their way. And the murder toll climbed. Journalists Stacy St. Clair and Christy Gutowski of the Chicago Tribune find something of their own –– one piece of the puzzle, hiding in plain sight.

For exclusive details about the Tylenol Murders and a transcript of this episode, visit www.chicagotribune.com/tylenolmurders.