After 300+ exonerations, and the attraction to forensics engendered by television series, one might think that the recovery of DNA at a crime scene – DNA that does *not* match the defendant – would quickly lead to acquittal. The contrary has occurred, however, particularly where a ‘good story’ to ‘explain’ the foreign DNA is told.
In NOTE: THE “ELASTICITY” OF DNA EVIDENCE? WHEN PROSECUTORIAL STORYTELLING GOES TOO FAR, 28 S. Cal. Rev. L. & Social Justice 138 (April, 2019), the following is reported:
In the recent psychological study, When Self-Report Trumps Science: Effects
of Confessions, DNA, and Prosecutorial Theories on Perceptions of Guilt,
Sara C. Appleby and Saul M. Kassin analyzed people’s perceptions of guilt
when presented with the following: a defendant who had confessed to a
crime, DNA evidence exculpating that defendant, and a prosecutor’s theory
explaining the contradictory evidence. Although the study confirms that
people are more persuaded by DNA than by confessions, participants in the
study were three times more likely to convict when a prosecutor offered an
explanation of why the exculpatory DNA conflicted with the confession than
when no explanation was presented.
The NOTE goes on to show that this occurs not just in the psychology lab but in the courtroom.
The Center on Wrongful Convictions has reported 19 known cases in which a
defendant confessed and was convicted despite exculpatory DNA, with
additional cases having been reported since then. In rape-murder cases, a
common prosecutorial theory used to override exculpatory DNA in the form of
semen is known pejoratively as “the unindicted co-ejaculator” theory. The
story advanced by prosecutors in these cases is that the victim had prior
consensual sex with an unknown male; afterward, the defendant raped her,
failed to ejaculate, and killed her. Prosecutors have also argued
necrophilia, conspiracy, and other questionable theories in order to
discount exculpatory DNA.
The proof of the potency of story-telling is in the guilty verdicts – the story triumphed over the science.