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.    

Our Partners

Federal Bureau of Investigations 

The Innocence Project 

Recent Exonerations

Briefs & Motions

See More

Practice Resources

See More

Trainings

  • Under the Microscope: Strategies for Implementing State & Local Microscopic Hair Comparison Reviews

See More

News

See More

Explore keywords to find information

RECENTLY ADDED & UPCOMING

  1. The Champion
    /Nacdl/media/image_library/StayInformed/Champion/ChampionCovers/March-April-2025.jpg?ext=.jpg

    March/April 2025

    What are the evidentiary implications of field sobriety tests in marijuana cases? Does the odor of marijuana give officers probable cause to search a vehicle?

  2. Amicus Brief
    /Nacdl/media/image_library/Elements/global/amicus.png

    Jenner & Block LLP v. U.S. Department of Justice

    Brief of the National Association of Criminal Defense Lawyers and New York Council of Defense Lawyers as Amici Curiae in Support of Plaintiff’s Motion for Summary Judgment.

  3. News Release
    /Nacdl/media/image_library/Elements/global/newsrelease.png

    News Release ~ Law Enforcement Executive Order

    NACDL Warns Executive Order's Dangerous Overreach Undermines Community Safety and Trust in Police – Washington, DC (April 29, 2025) – The National Association of Criminal Defense Lawyers (NACDL) expressed deep concern regarding the Executive Order titled "Strengthening and Unleashing America’s Law Enforcement to Pursue Criminals and Protect Innocent Citizens," cautioning that several of its proposals represent a dangerous overreach that undermines these goals by jeopardizing individual rights and the legitimacy of law enforcement in the eyes of the community.

  4. Event
    /Nacdl/media/image_library/Learn/nacdlcleinstitute/2025_Post-Dobbs_Trial_Tactics_2025-02-26_v02_Event-Listing_2.jpg?ext=.jpg

    Trial Tactics for Pregnancy-Related Cases: Skills for Every Defender

    LOCATION: The University of Texas School of Law, Austin, TX
    DATE: May 16-17, 2025
    COST: FREE (registration is required)
    CLE Credit: Up to 14.5 credits 

  5. Webinar
    /assets/img/nacdl_og.png

    Collaborative Approaches to Appellate Defense: Recognizing Clients' Legal Expertise

    WHEN: Thursday, May 8, 3:00-4:30pm ET / 12:00-1:30pm PT
    CLE CREDIT: not available
    COST: Free

Featured Products