United States v. Davis

Earl Davis (defendant) was charged with robbery and murder for his role in the robbery of an armored bank vehicle and the resulting death of the passenger. Investigators recovered DNA samples from the steering wheel of the perpetrators’ getaway car and from a hat that one of the shooters had left at the scene. The DNA samples were entered into a nationwide database and returned a match with Davis’s DNA. The match was a “cold hit” because Davis had not been linked to the crime by other evidence prior to the match. The testing laboratory determined that, in the absence of an identical twin, Davis was the source of the DNA on the steering wheel and the hat to a reasonable degree of scientific certainty. The prosecution introduced an affidavit of a Federal Bureau of Investigation (FBI) employee stating that the FBI permitted this type of source attribution only if the probability of a random profile match was less than 1 in 300 billion. Davis filed a motion to exclude the DNA evidence, arguing that there was no single, universally accepted methodology for calculating the probability that a cold match was random. There were three established methodologies for this type of calculation that could provide the proper context of a cold match. Each methodology was statistically reliable, but answered a distinct question. There was disagreement in the scientific community as to which methodology provided the best context for cold-hit matches. In support of his motion, Davis argued that the DNA evidence should be excluded because of this disagreement. Davis also argued that a source-attribution statement was per se inadmissible.