Forensic Flaws and Wrongful Convictions. Edwin Colfax The Justice Project October 8, 2010. An Anecdote. . . . Related by Evan Hodge, former chief of the FBI Firearms and Toolmark Unit:
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The Justice Project
October 8, 2010
Related by Evan Hodge, former chief of the FBI Firearms and Toolmark Unit:
A detective goes to a ballistics expert along with a .45 pistol and a bullet recovered from a murder victim.
“We know this guy shot the victim and this is the gun he used. All we want you to do is confirm what we already know so we can get a warrant to get the scumbag off the street. We will wait. How quick can you do it?”
The analyst conducted tests and provided a finding that linked the slug to the gun.
The suspect was confronted with this damning forensic evidence in an interrogation that ended with his confession.
The defendant then led the police to a different .45 pistol, which tests later showed was the true murder weapon.
-- Evan Hodge, Guarding Against Error, 20 Ass’n Firearms & Toolmark Examiners’ J. 290, 292 (1988).
In more than 50% of DNA exonerations, unvalidated or improper forensic science contributed to the wrongful conviction, making it the second most prevalent factor contributing to wrongful convictions.
In 60% of DNA exoneration cases, “forensic analysts called by the prosecution provided invalid testimony at trial, that is, testimony with conclusions misstating empirical data or wholly unsupported by empirical data.”
-Garrett/Neufeld Study: Invalid Forensic Science Testimony and Wrongful Convictions, Virginia Law Review, March 2009.
DNA demonstrates the power of forensic science and exposes previously unrecognized limitations of forensic science.
The overwhelming majority of criminal cases are not amenable to DNA testing.
Over-representation of certain kinds of cases: rape and, to a lesser degree, murder.
Discovered wrongful convictions represent only a tiny fraction of criminal convictions, BUT the discovered error is not all of the error.
In non-DNA cases, the innocent have a very difficult, virtually insurmountable burden.
While the true rate of wrongful conviction is difficult to know, we should be focusing on the fact that much (not all) of this error is preventable. We have identified patterns of preventable error.
The costs of wrongful conviction are so grave and profound – loss of liberty, public safety, collateral damage, financial—that we must take all reasonable steps to reduce the risk.
Eg. - Fred Zain (WV, TX), Joyce Gilchrist (OK),
Ralph Erdmann (TX)
Invalid Forensic Science Testimony and Wrongful Convictions, Virginia Law Review, March 2009.
There were a total of 72 different analysts who presented invalid forensic testimony against a person that would later be proven demonstrably innocent.
They worked for 52 different labs, in 25 states.
“The adversarial process largely failed to police this invalid testimony. Defense counsel rarely cross-examined analysts concerning invalid testimony, and rarely obtained experts of their own.”
Most fell into 2 categories:
1. Serology (Analysis of bodily fluids to determine blood type characteristics). Type A/B/O, plus “secretor status” – whether a person secretes blood type substances into bodily fluids (eg. saliva or semen) or not.
2. Microscopic Hair Comparison (MHC) – The visual comparison of questioned hairs from a crime scene and known exemplars to determine presence of shared characteristics.
1.Misuse of empirical population data.
Example, Gary Dotson – Testimony that Dotson was among 11% that could have been the donor, when in fact it was 100%.
2. Unsupported conclusions about the probative value of evidence (eg. providing opinions on the significance of evidence without any empirical support).
Cannot say that in all the cases where bad forensic testimony occurred that it “caused” the wrongful conviction, since there was usually other kinds of evidence involved, such as an eyewitness identification, that was presented.
Could the presence of other evidence have contributed to the faulty interpretation and testimony? (We tend to see/find what we expect or desire to find, or what makes the most sense given other things that we know.)
Dog scent line-ups
Bullet lead analysis
This is not to suggest that there are not valid and reliable methods that have a subjective interpretive element.
Rather, where there is a subjective interpretive element, there is real risk of inadvertent contextual bias that must be addressed.
In Dror’s initial study, experienced analysts were asked to evaluate a series of fingerprints to determine if they matched. Though the analysts believed the prints were for an actual, open case, they were actually reexamining prints they had correctly evaluated in the past, this time accompanied by artificial contextual information, such as that the suspect had confessed. The results were striking. In cases where analysts were given contextual information about the fingerprints, they were wrong in almost seventeen percent of the cases. These errors were particularly notable because the same analysts had previously evaluated the prints correctly.