After the experiment was over, he realized that the reason he had not noticed a reaction from the medicine was that he was part of the control group.
During the senior project the students used a control group to get a general understanding of how people responded to oddly dressed mannequins, the control group gave the students a starting point for the study.
The Stanford Prison Experiment was an interesting concept, however, the lack of a control group invalidate almost all of its scientific findings.