Eighty years ago this week, inventor Leonarde Keeler proudly proclaimed his expert testimony before a Wisconsin jury to be “a signal victory for those who believe in scientific crime detection.”

One of the creators of the modern-day polygraph, the man named after Leonardo da Vinci by his father in the hopes that he would do similarly great things, had just presented his findings in the case of Cecil Loniello and Tony Grignano, two young men on trial for the attempted murder of a police officer as they fled the scene of a robbery. The judge in the case had sought out the polygraph because of the technology’s showing at the 1933 World’s Fair police exhibit. Both sides had agreed to allow the test—the defendants saw little to lose and the prosecution was armed with only circumstantial evidence and two untrustworthy witnesses.

Keeler strapped his lie detector to each man’s chest and arm. When Loniello was asked whether he shot the sheriff, the needle recorded a violent fluctuation indicating a change in breathing, a sudden increase in blood pressure, and a rise in pulse. When asked whether he was driving the car, all systems were normal. The results told Keeler and his colleague, Fred Inbau, not only that the two men were both guilty and lying, but revealed each man’s role in the crime. Science, it seemed, had triumphed.