https://www.ncjrs.gov/txtfiles/dnaevid.txt

Postconviction DNA exonerations provide a remarkable opportunity to reexamine, with greater insight than ever before, the strengths and weaknesses of our criminal justice system and how they bear on the all-important question of factual innocence. The dimensions of the factual innocence problem exceed the impressive number of postconviction DNA exonerations listed in this report. Indeed, there is a strong scientific basis for believing these matters represent just the tip of a very deep and disturbing iceberg of cases. Powerful proof for this proposition lies with an extraordinary set of data collected by the Federal Bureau of Investigation (FBI) since it began forensic DNA testing in 1989.

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 dispositive.

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.

Without DNA testing, the prospects of wrongful convictions in these exclusion cases are evident. Even if one assumes half the normal conviction rate (State conviction rates for felony sexual assaults average about 62 percent), one would expect that hundreds of people who have been exonerated by FBI DNA testing in sexual assault cases over the last 7 years would have otherwise been convicted.