Problems with Forensic Methods

Back to Forensic Science

DNA Evidence and Wrongful Convictions
  • Overturning Wrongful Convictions Involving Misapplied Forensics (Innocence Project)
    • “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.”
  • Forensic Science in Criminal Courts (PCAST)
    • “Ironically, it was the emergence and maturation of a new forensic science, DNA analysis, that first led to serious questioning of the validity of many of the traditional forensic disciplines. When defendants convicted with the help of forensic evidence from those traditional disciplines began to be exonerated on the basis of persuasive DNA comparisons deeper inquiry into scientific validity began.”
  • DNA Profiling provides a way of evaluating other forensic methods.
Potential Problems
  • For forensic evidence to have probative value
    • The evidence must be generated by a reliable forensic method
    • The forensic method must be properly and impartially applied
    • The evidence must be accurately and impartially presented in court
  • There are thus three kinds of potential problems with forensic evidence.
    • A forensic method may be unreliable or not proven reliable.
    • A forensic method may be improperly applied or affected by bias, especially confirmation bias.
    • Forensic evidence may be misrepresented in court.

PCAST Report

View PCAST Report

Bullet-Lead Analysis
  • The theory of Bullet-Lead Analysis is that every batch of bullets has a chemical makeup that enables an individual bullet to be traced back to the batch or even to a specific box.
  • The FBI used the method for over four decades, starting with the Kennedy assassination in 1963.
  • The FBI asked the National Academy of Sciences (NAS) to study Bullet-Lead Analysis. The 2004 NAS report found that
    • there was no scientific basis for determining that a bullet came from a specific box of ammunition
    • there was insufficient data to support drawing the conclusion that a bullet came from a particular batch of ammunition
  • The FBI discontinued Bullet-Lead analysis in 2005
Hair Analysis
  • In 2002, FBI scientists used mitochondrial DNA sequencing to re-examine 170 microscopic hair comparisons that the agency’s scientists had performed in criminal cases. The DNA analysis showed that, in 11 percent of cases in which the FBI examiners had found the hair samples to match microscopically, DNA testing of the samples revealed they actually came from different individuals.
  • In 2015 The Justice Department and FBI formally acknowledged that nearly every examiner in an elite FBI forensic unit gave flawed testimony in almost all trials in which they offered evidence against criminal defendants over more than a two-decade period before 2000.
  • The review confirmed that FBI experts systematically testified to the near-certainty of “matches” of crime-scene hairs to defendants, backing their claims by citing incomplete or misleading statistics drawn from their case work.
Bitemark Analysis
From PCAST Report
  • “A 2010 study of experimentally created bitemarks produced by known biters found that skin deformation distorts bitemarks so substantially and so variably that current procedures for comparing bitemarks are unable to reliably exclude or include a suspect as a potential biter. (“The data derived showed no correlation and was not reproducible, that is, the same dentition could not create a measurable impression that was consistent in all of the parameters in any of the test circumstances.) “
  • “A recent study by the American Board of Forensic Odontology also showed a disturbing lack of consistency in the way that forensic odontologists go about analyzing bitemarks, including even on deciding whether there was sufficient evidence to determine whether a photographed bitemark was a human bitemark.”
  • “In February 2016, following a six-month investigation, the Texas Forensic Science Commission unanimously recommended a moratorium on the use of bitemark identifications in criminal trials, concluding that the validity of the technique has not been scientifically established.”
  • “PCAST finds that bitemark analysis does not meet scientific standards for foundational validity, and is far from meeting such standards.  To the contrary, available scientific evidence strongly suggests that examiners cannot consistently agree on whether an injury is a human bite-mark or cannot identify the source of the bite-mark with reasonable accuracy.”
  • Convicted of rape and murder based on a bite-mark “match,” Robert DuBoise was released after 37 years in prison after DNA evidence excluded him. (WaPo)
Blood Spatter Analysis
Strengthening Forensic Science (NAS)

“Scientific studies support some aspects of bloodstain pattern analysis. One can tell, for example, if the blood spattered quickly or slowly, but some experts extrapolate far beyond what can be supported. Although the trajectories of bullets are linear, the damage that they cause in soft tissue and the complex patterns that fluids make when exiting wounds are highly variable. The uncertainties associated with bloodstain pattern analysis are enormous.”

Case of Joe Bryan
  • New York Times He Has Spent Three Decades in Prison. Now Experts Dispute the Evidence.
    • “The findings of the Texas Forensic Science Commission, a national leader in forensic science reform, called into question the conviction of Joe Bryan, who has now spent more than 30 years in prison for murdering his wife in 1985.
    • Created by the Texas Legislature in 2005, the commission — made up of seven scientists, one prosecutor and one defense attorney — does not investigate the guilt or innocence of defendants, but rather the reliability and integrity of the forensic science used to win their convictions. 
    • Ms. Rossi found that the detective misstated scientific concepts, used flawed methodology and incorrectly interpreted evidence. Both his analysis and his expert testimony were not scientifically accurate, she told the commission, and could not be supported by published research or data. 
    • Adam Sibley, the Bosque County district attorney, has so far successfully blocked Mr. Bryan’s efforts to have DNA analysis performed on previously untested evidence.”
    • “The Bryan case has already spurred forensic science reform. In February, the commission sought to end the practice of allowing law enforcement officers with minimal training in bloodstain-pattern analysis to testify in Texas, stipulating that such analysis must be performed by an accredited organization if it is to be allowed in court. The decision is expected to prompt other states to follow suit, as the commission’s reforms often do.”
  • ProPublica 33 Years After Dubious Evidence Helped Convict Him, Joe Bryan Has Been Released on Parole