Leonarde Keeler administers polygraph tests to two murder suspects, the first time polygraph evidence was admitted in U.S. courts.

Leonarde Keeler was an American inventor best known for co-inventing the polygraph. He was named after the polymath Leonardo da Vinci, and preferred to be called Nard. He was a Berkeley high school student and amateur magician. He was captivated by John Augustus Larson's machine, a "cardio-pneumo psychogram", with the goal of detecting deception, and worked on it to produce the modern polygraph.

A polygraph, often incorrectly referred to as a lie detector test, is a pseudoscientific device or procedure that measures and records several physiological indicators such as blood pressure, pulse, respiration, and skin conductivity while a person is asked and answers a series of questions. The belief underpinning the use of the polygraph is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers; however, there are no specific physiological reactions associated with lying, making it difficult to identify factors that separate those who are lying from those who are telling the truth.