The Stanford prison experiment, a prison simulation that took place over two weeks in 1971, forever shifted the field of psychology and its interpretation of human nature. Now, a new docuseries by National Geographic delves into the study and features firsthand accounts from the original “guards” and “prisoners,” many speaking on camera for the first time.

Directed by Juliette Eisner, The Stanford Prison Experiment: Unlocking the Truth explores a new narrative examining the motives of Dr. Philip Zimbardo, the Stanford University psychology professor who oversaw the experiment and gained worldwide recognition following its conclusion.