Wednesday, August 28, 2013

A hard fact for anyone concerned about rape convictions and false accusations

From Convicted by Juries, Exonerated by Science: Case Studies in the Use of DNA Evidence to Establish Innocence After Trial | National Institute of Justice:
Every year since 1989, in about 25 percent of the
sexual assault cases referred to the FBI where
results could be obtained (primarily by State and
local law enforcement), the primary suspect has
been excluded by forensic DNA testing.
Specifically, FBI officials report that out of
roughly 10,000 sexual assault cases since 1989,
about 2,000 tests have been inconclusive (usually
insufficient high molecular weight DNA to do
testing), about 2,000 tests have excluded the
primary suspect, and about 6,000 have "matched" or
included the primary suspect.1 The fact that these
percentages have remained constant for 7 years, and
that the National Institute of Justice's informal
survey of private laboratories reveals a strikingly
similar 26-percent exclusion rate, strongly
suggests that postarrest and postconviction DNA
exonerations are tied to some strong, underlying
systemic problems that generate erroneous
accusations and convictions.

It must be stressed that the sexual assault
referrals made to the FBI ordinarily involve cases
where (1) identity is at issue (there is no consent
defense), (2) the non-DNA evidence linking the
suspect to the crime is eyewitness identification,
(3) the suspects have been arrested or indicted
based on non-DNA evidence, and (4) the biological
evidence (sperm) has been recovered from a place
(vaginal/rectal/oral swabs or underwear) that makes
DNA results on the issue of identity virtually

It is, of course, possible that some of the FBI's
sexual assault exclusions have included false
negatives. False negatives could occur, for
example, because of (1) laboratory error; (2)
situations where the victim of the assault conceals
the existence of a consensual sexual partner within
48 hours of the incident and the accused suspect
did not ejaculate (if the suspect ejaculated, the
DNA should be identified along with the undisclosed
sexual partner); or (3) multiple assailant sexual
assault cases where none of the apprehended
suspects ejaculated (the FBI counts the exclusion
of all multiple suspects in a case as just one
exclusion). Nonetheless, even with these caveats,
it is still plain that forensic DNA testing is
prospectively exonerating a substantial number of
innocent individuals who would have otherwise stood
trial, frequently facing the difficult task of
refuting mistaken eyewitness identification by a
truthful crime victim who would rightly deserve
juror sympathy.
Recommended: The Innocence Project - DNA Exonerations Nationwide