Fingerprint Fallability

Law professor Jennifer Mnookin argues that, as our database of fingerprints grows, we’re finding that identification based on fingerprints is not nearly as foolproof as we once thought.

What is truly remarkable is that we simply do not know how often different people’s prints may significantly resemble one another, or how good examiners are at distinguishing between such prints. DNA profiling provides what is called a “random match probability” — the odds that the DNA of someone picked at random would match the profile in question. With fingerprinting, we entirely lack the information to provide an equivalent statistic. Yet without this knowledge we cannot accurately evaluate the evidentiary value of a supposed fingerprint match.


Fingerprint identification as it is now practiced is not like a double-blind scientific study. Examiners, typically law-enforcement employees, are frequently privy to outside knowledge about a case, which creates a genuine risk that their examination will inadvertently be contaminated. There is simply no excuse for failing to develop internal procedures to protect examiners from extraneous knowledge.

Until now, many people in the field of fingerprinting have defensively resisted calls for additional research and investigation of fingerprinting. Because experts are permitted to testify about “100 percent positive” matches and to claim in court an error rate for the technique of zero, they have little incentive to support any research.


FILED UNDER: Law and the Courts
James Joyner
About James Joyner
James Joyner is Professor and Department Head of Security Studies at Marine Corps University's Command and Staff College. He's a former Army officer and Desert Storm veteran. Views expressed here are his own. Follow James on Twitter @DrJJoyner.