Visualizing DNA Proof

Abstract

DNA proof inherently involves the use of probability theory, which is often counterintuitive. Visual depictions of probability theory, however, can clarify the analysis and make it tractable. A DNA hit from a large database is a notoriously difficult probabi­li­ty theory issue, yet the visuals should enable courts and juries to handle it. The Puckett facts are an example of a general approach: A search in a large DNA database produces a hit for a cold crime from 1972 San Francisco. Probability theory allows us to process the probabilities that someone else in the database, someone not in the database, or the initial suspect, Baker, may be the perpetrator and obtain the probability of Puckett’s guilt. Given the clarity of this analysis, decisions that do not follow it deserve reversal as clearly erroneous.