Fingerprints aren’t proof. Despite its aura of infallibility, courtroom claims of fingerprints’ uniqueness are slowly receding
Scientist Nancy Knight documented snowflakes in 1988 while studying cirrus clouds for the National Center for Atmospheric Research. During a Wisconsin snowstorm she found two identical sets of snow crystals – identical under a microscope, at least – giving lie to the old belief that no two snowflakes are alike. That aura of uniqueness also surrounds the arches, loops, and whorls at the tips of our fingers, and to this day most fingerprint examiners remain steadfast that no two fingerprints are exactly alike.
“Fingerprint examiners typically testify in the language of absolute certainty,” professor Jennifer Mnookin at the University of California Los Angeles has written. But like many other claims for forensic science, the assertion that fingerprints are unique lacked a solid scientific basis and now is viewed with new caution.
“The language of certainty that examiners are forced to use hides a great deal of uncertainty,” the U.K.’s Lord Justice Leveson put it when addressing the Forensic Science Society.
Or as Penn State Dickinson School of Law professor David Kaye observed in a 2010 news release, “Fingerprint examiners and other forensic experts often testify with ’100% confidence’ or to a ‘scientific certainty’ that a defendant is the source of a latent fingerprint or that a bullet came from a particular gun. It is time for criminalists to provide more scientifically defensible-and legally palatable-testimony.”