Hair of the dog: Why the Federal Rules of Evidence Should be Adjusted to Require Clearer and Stricter Scientific Validation of Expert Evidence
Emily Karwacki, Staff Editor
November 15, 2024
Most people know what forensic science is thanks to the many television shows and movies where they see scientists in lab coats looking through microscopes, analyzing fingerprints or fibers, and providing evidence to put the bad guy behind bars. In reality, forensic science is “the application of scientific or technical practices to the recognition, collection, analysis, and interpretation of evidence for criminal and civil law or regulatory issues.”[1] Forensic evidence’s admission to courtrooms is often governed by the Federal Rules of Evidence Rule 702. Rule 702 essentially states that a qualified expert witness can testify if it is more likely than not that “(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.”[2] While these methods may seem infallible, and indeed are often stated by “experts” to be so, they are far from perfect and have been causing wrongful convictions for decades.[3]
The issue with some forensic science methods in the courtroom is that many of them have not been rigorously tested. This means that we do not know whether these methods are even remotely accurate. In courts, the Frye standard emerged in 1923 and stated that scientific evidence needed to have gained general acceptance in the particular field to which it belonged to be allowed in the courtroom.[4] The Federal Rules of Evidence came along in 1975 allowing scientific evidence or fact into the courtroom if it would help the jury understand the evidence or determine the fact at issue and the witness was qualified. Then the Supreme Court decided in 1993 that trial judges were to be the gatekeepers of expert evidence[5] and only evidence that has been tested, peer reviewed or published, and had standards, and was generally accepted should be allowed.[6]
Forensic methods such as hair analysis, 911 calls, blood-pattern analysis, bite mark analysis, fingerprint analysis, and roadside drug tests have been challenged numerous times and even debunked. But courts still allow juries to hear such evidence.[7] For example, experts regularly testify that a match of 5-15 points on a human fingerprint is enough to identify a perpetrator.[8] However, there are 75-125 points that can be compared on a fingerprint and no research has been done to show if that low bar is sufficient.[9] This means we have sent people to prison on as little as a 6.7% match with no idea if that is enough. In one disturbing case, a man was sent to prison for 28 years based on hair analysis placing him at the scene of a murder. He was declared innocent however when it came to light some of the hairs the FBI assured a jury were his were actually dog hairs.[10] Many advanced courses for forensic methods like fingerprint analysis are offered to law enforcement. The courses claim to provide sufficient foundation for officers to testify as “expert” witnesses in the courtroom despite requiring as little as one week of education. Such courses include forensic clothing examination, forensic pathology, cognitive interview and statement analysis, latent fingerprint comparison and analysis, and arson investigation.[11]
Multiple government reports point to the need for more rigorous testing of forensic methods, but little progress has been made.[12] As per the National Research Council, copious forensic evidence is introduced into trials without any meaningful scientific validation or reliability testing.[13] The President’s Council of Advisors on Science and Technology also found forensic methods lacking validity and reliability.[14] The Council thoroughly reviewed available literature and received input from the FBI Laboratory, judges, prosecutors, advocates, and leading industry and academic scientists. The report recommended that forensic methods should have clear error rates and should be empirically tested through blind testing (no researcher knows what the correct answer is), with sufficiently large numbers of samples and scientists, and making the data publicly available.[15] At a minimum, to usefully testify about items sharing a source (this would include fingerprint, blood-pattern, bite mark, firearm mark, hair comparison, and more), a witness should need to tell the trier of fact how often items with the observed similarities are actually a match (i.e., provide an error rate).[16]
Unfortunately, law enforcement does not want to stop using these methods because they help them catch suspects and judges are hesitant to overturn precedent.[17] Proponents may claim these forensic methods can simply be dissected on cross-examination if the results are so dubious. However, once a witness is set up as an “expert” their credentials and the credibility of their opinion has already been established and are difficult to tear down.[18] We should not be relying on opposing council, who is likely not a scientist, to convince a jury that the expert they just heard is wrong. The Department of Justice and some presidential administrations have also delayed progress saying that these reports are attacks on forensic science.[19] This is despite the DOJ stating in 2015 that 90% of its cases relying on microscopic hair analysis amounted to false testimony because of the inaccuracy of the method.[20] Further, between 1989 and 2019 the National Registry of Exonerations documented 553 cases where someone was wrongfully convicted based on questionable forensic evidence and later found innocent.[21] This is certainly a far cry from Sir Blackstone’s maxim that “it is better that ten guilty persons escape than that one innocent suffer.”
The best way forward would be to adjust the Federal Rules of Evidence once again to reflect the importance of testable, valid scientific evidence. A clearer rule might look like “a witness who is qualified by experience, training, and education may testify in court if the proponent demonstrates that the methods used by the expert were (a) subjected to rigorous testing, (b) produce an error rate of at most 5%, (c) have been validated by other scientists using blind testing, and (d) the testimony reflects a reliable application of the method to the specific facts of the case.” Implementation of this rule could decrease rates of wrongful conviction, push forensic scientists to adopt rigorous testing methods, and decrease corruption from self-proclaimed forensic “experts” willing to say anything on the stand.
[1] President’s Council of Advisors on Science and Technology, Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods 1 (2016).
[2] Fed. R. Evid. 702.
[3] Matthew Scherb, Untested Forensic Sciences Present Trouble in the Courtroom, American Bar Association (February 5, 2019), https://www.americanbar.org/groups/judicial/publications/appellate_issues/2019/winter/untested-forensic-sciences-present-trouble-in-the-courtroom/.
[4] President’s Council, supra note 1, at 41.
[5] Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).
[6] President’s Council, supra note 1, at 41.
[7] Sophia Kovatch et al., Is It Forensic Science or Is It Junk Science?, ProPublica (Jan. 31, 2023), https://www.propublica.org/article/understanding-junk-science-forensics-criminal-justice; The Institute of Criminal Justice Training Reform, Junk Science (Last visited October 28, 2024), https://www.trainingreform.org/junk-science.
[8] Scherb, supra note 3.
[9] Id.
[10] Nemann Law Offices, FBI forensics convicted innocent man for 28 years claiming dog hair was his (last visited November 9, 2024), https://www.nemannlawoffices.com/blog/fbi-forensics-convicted-innocent-man-for-28-years-claiming-dog-hair-was-his.cfm.
[11] Junk Science, supra note 4.
[12] President’s Council, supra note 1; National Research Council, Strengthening Forensic Science in the United States: A Path Forward (2009).
[13] National Research Council, supra note 8, at 108.
[14] President’s Council, supra note 1, at 1.
[15] President’s Council, supra note 1; National Research Council, supra note 8, at 46, 53.
[16] Scherb, supra note 3.
[17] Jon Schuppe, ‘We are going backward’: How the justice system ignores science in the pursuit of convictions, NBC News (Jan. 23, 2019), https://www.nbcnews.com/news/us-news/we-are-going-backward-how-justice-system-ignores-science-pursuit-n961256.
[18] Scherb, supra note 3.
[19] Id.
[20] Innocence Project, FBI Testimony on Microscopic Hair Analysis Contained Errors in at least 90% of Cases in Ongoing Review (last visited November 9, 2024) https://innocenceproject.org/fbi-testimony-on-microscopic-hair-analysis-contained-errors-in-at-least-90-of-cases-in-ongoing-review/.
[21] Id.