Microscopic Hair Comparison Analysis

This page contains materials and information related to Microscopic Hair Comparison Analysis and NACDL's extensive work in the area.

To date, more than 300 people have been proven innocent through DNA testing, which in most cases did not exist or was not available at the time of their convictions.  In almost ¼ of the DNA exonerations (just over 70 defendants), the prosecution used hair microscopy evidence to link the defendant to the crime.  Advances in science, specifically the advent of mitochondrial DNA testing (DNA testing on hair without a root), revealed that examiners reported false hair matches in those specific cases.   

For decades, the FBI Crime Lab has conducted hair microscopy, where an examiner uses a high powered microscope to view hair from a crime scene and compare it to a known hair sample.  Looking for similarities in each hair, if enough characteristics are the same, the examiner deems the hair a “match”.  Further, in making comparisons, examiners use a “sample” (approximately 10) hairs from the known subject to compare with an unknown hair to see if characteristics from the unknown hair are present in the array of known hairs.  Thus, it is not a one to one comparison, but rather a one (unknown hair) to many (known hair sample) comparison to search for similar characteristics.  

Scientists have criticized this forensic discipline and noted its limited reliability based, in part, on the unknown pool of subjects with the same hair characteristics.  In the late 1990s, and the use of mitochondrial DNA testing, the FBI crime lab limited its use of hair microscopy and used it only in conjunction with DNA testing to confirm results.    

Following a trio of DNA exonerations in Washington DC (from 2009-2012), all three defendants were convicted on FBI microscopic hair comparison evidence which turned out to be wrong, the FBI commenced an internal review of microscopic hair analysis cases to determine the extent to which flawed evidence may have tainted convictions. The FBI estimates that approximately 21,000 cases involved microscopic hair analysis will be reexamined.  In July of 2012, the Department of Justice publicly announced this historical review and noted that the review will include collaboration with the Innocence Project and NACDL.  The involvement of prominent defense organizations is vital for two reasons: it underscores the non-adversarial nature of the review process and it facilitates the identification of those who were affected by the flawed evidence and the procurement of transcripts essential to the review process.  

The review begins internally at the FBI crime lab identifying cases with a “positive” association of hair analysis (allegedly linking the defendant to the crime scene or to the victim).  Next, the FBI reviews the lab reports and the trial testimony from the FBI examiner (if the defendant went to trial rather than pled guilty).  The reviewers identify errors in the reports and/or testimony:  “errors” involve statements exceed the limits of science and/ or overstate the conclusions that may appropriately be drawn from a “positive association” between evidentiary hair and a known hair sample.  Once errors are identified by the reviewers at the FBI lab, the results are sent to the IP and NACDL for independent review.  Ultimately, a report is generated identifying the errors in the lab report and/or trial testimony, and the defendant is notified via current counsel or last known counsel.    

Due to the nature of post-conviction review, the majority of the affected defendants no longer have an attorney and most are not entitled to an attorney at the government’s expense.  Thus, NACDL has committed to finding counsel, on a pro bono basis, to review cases identifying any potential post-conviction claims a defendant may bring (under the appropriate state or federal post-conviction relief law) and represent those defendants in court.    

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