Overturning Wrongful Convictions Involving Flawed Forensics

The Problem:

The misapplication of forensic science contributed to 45% of wrongful convictions in the United States proven through DNA evidence. False or misleading forensic evidence was a contributing factor in 24% of all wrongful convictions nationally, according to the National Registry of Exonerations, which tracks both DNA and non-DNA based exonerations.1

This includes convictions based on forensic evidence that is unreliable or invalid and expert testimony that is misleading. It also includes mistakes made by practitioners and in some cases misconduct by forensic analysts. In some cases, scientific testimony that was generally accepted at the time of a conviction has since been undermined by new scientific advancements in disciplines including:

  • Hair comparisons: Microscopic hair analysis involves comparing hair found at a crime scene with the hair of the defendant. A 2009 National Academy of Sciences report stated that microscopic hair comparisons could not be used to match hair with a specific individual.2 In 2015 the FBI announced that its hair microscopy experts overstated the probability of a match between hair evidence and the defendant’s hair in 95 percent of the 268 cases it had reviewed.3
  • Arson: Two decades of fire research has debunked evidence that was used to convict people of arson. The 1992 publication of National Fire Protection Association (NFPA) 921 noted that many of the physical artifacts previously thought to occur only in intentional fires—such as “alligatoring” of wood, crazed glass, and sagged furniture springs—could actually occur in accidental fires.NFPA 921 only became generally accepted by the relevant scientific community in the early 2000’s.
  • Comparative Bullet Lead Analysis: Comparative Bullet Lead Analysis (“CBLA”) was believed to be able to link bullets found at a crime scene to bullets possessed by a suspect based on the assumption that the lead composition in a bullet was unique and limited to the batch that it came from. Since the early 1980’s the FBI conducted bullet lead examined in over 2,500 cases. The FBI stopped using CLBA after a 2002 National Academy of Sciences (NAS) report found problems with interpretations of the results of these analyses.5

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Challenges in Getting Back into Court When Science Changes

Because shifts in scientific understanding often take decades to emerge, individuals whose wrongful convictions were based on misapplied science might face difficulties in proving their innocence due to time limitations and high evidentiary standards. In addition, some state courts do not recognize discredited scientific evidence as new evidence of a wrongful conviction.

It is critical that there be a mechanism for the wrongfully convicted to get back into court to prove their innocence if the forensic evidence used to convict them is undermined by new scientific advancements, guidelines, or repudiation of expert testimony.

Reforming Laws to Ensure Access to Relief Based on Changes in Science

Currently, five states have enacted laws to clarify that wrongfully convicted people can get back into court based on discredited forensic evidence:

  • California: Since the law was enacted in 2014, a total of 14 petitions have been filed by the Northern California Innocence Project, California Innocence Project and Loyola Law School for the Innocent.
  • Connecticut: In 2018, Connecticut enacted a law removing the 3-year time limit in the motions for new trial law to permit the introduction of new, non-DNA evidence after conviction. The new law includes a provision to clarify that new evidence may include new scientific research, guidelines, or expert recantation.
  • Michigan: In 2018, Michigan amended its court rule that dictates post-appeal relief. The changes now allow a person to file a post-conviction motion for relief based on new scientific evidence, including but not limited to: shifts in a field of scientific knowledge, changes in expert knowledge or opinion, and shifts in a scientific field used in a conviction.
  • Texas: All petitions filed under the law go to the Court of Criminal Appeals, which has received a total of 25 petitions since the law was enacted in 2013.
  • Wyoming: In 2018, Wyoming enacted a ‘factual innocence’ law to remove the state’s two-year time limit for introducing new, non-DNA evidence. The law includes a provision which clarifies that new evidence may include new scientific research, guidelines or expert recantations that undermine forensic evidence used for convictions.


[1] “Browse the National Registry of Exonerations.” The National Registry of Exonerations.

[2] National Academy of Sciences, “Strengthening the Use of Forensic Science in Criminal Courtrooms.” 2009.

[3] Hsu, Spencer. “FBI Admits Flaws in Hair Analysis over Decades.” The Washington Post. April 18, 2015.

[4] National Fire Protection Association, “Guide for Fire and Explosion Investigations 1992 Edition.” 1992.

[5]  “FBI Laboratory Announces Discontinuation of Bullet Lead Examinations.” FBI. September 01, 2005.

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