Pudd'nhead Wilson (1916)

In the mid-19th century, lawyer Pudd'nhead Wilson suffers the mockery of the community because of his obsession with fingerprints. Two of his samples are the infant prints of Tom Driscoll, the son of a white woman, and Chambers, whose mother is a mulatto nurse. Both boys have the same father, however, and both are about the same age, and after their birth, Roxy, angry at the Driscolls, switches them. Then, the false Tom murders his uncle and tries to blame his valet for the crime. Pudd'nhead defends the accused, and while comparing new fingerprint samples against the old, discovers the switch that was made years before. He then convinces an initially doubting jury to accept the infallibility of fingerprint evidence, after which the real Tom is restored as the Driscoll heir and the false one goes to jail.