Unvalidated or Improper Forensic Science

Many forensic techniques — such as hair microscopy, bite mark comparisons, firearm tool mark analysis and shoe print comparisons — have not been subjected to sufficient scientific evaluation and have resulted in error.

Since the late 1980s, DNA analysis has helped identify the guilty and exonerate the innocent nationwide. While DNA testing was developed through extensive scientific research at top academic centers, many other forensic techniques — such as hair microscopy, bite mark comparisons, firearm tool mark analysis and shoe print comparisons — have not been subjected to sufficient scientific evaluation. Meanwhile, forensics techniques that have been properly validated — such as serology, commonly known as blood typing — are sometimes improperly conducted or inaccurately conveyed in trial testimony. In some cases, forensic analysts have fabricated results or engaged in other misconduct.

All of these problems constitute unvalidated or improper forensic science, which is the second-greatest contributor to wrongful convictions that have been overturned with DNA testing. In about half of DNA exonerations, unvalidated or improper forensic science contributed to the wrongful conviction. Click here for a complete table with information on each case where unvalidated or improper forensic science contributed to a wrongful conviction that was later overturned with DNA testing.

Click here for information on how unvalidated or improper forensic science contributed to a wrongful conviction that was later overturned with DNA testing, broken down by discipline.

While DNA exonerations are a window into the effect of unvalidated or improper forensic science contributing to wrongful convictions, DNA does not solve the problem. In fact, experts estimate that only 5-10% of all criminal cases involve biological evidence that could be subjected to DNA testing. In the other 90-95% of crimes, DNA testing is not an option – so the criminal justice system relies on other kinds of evidence, including forensic disciplines that may not be scientifically sound or properly conducted.

The Absence of Scientific Standards

Unlike DNA testing, many forensic disciplines – particularly those that deal with comparing impression marks and objects like hair and fiber – were developed solely to solve crime. These disciplines have evolved primarily through their use in individual cases. Without the benefit of sufficient foundational research or adequate financial resources, applied research has also been minimal.

In fact, many forensic testing methods have been applied with little or no scientific validation and with inadequate assessments of their robustness or reliability. Furthermore, they lacked scientifically acceptable standards for quality assurance and quality control before their implementation in cases.

Although there have been positive developments in forensic science in recent years, our cases have shown that forensic analysts sometimes testify without a proper scientific basis for their findings. Testimony about more dubious forensic disciplines, such as efforts to match a defendant’s teeth to marks on a victim or attempts to compare a defendant’s voice to a voicemail recording, are cloaked in science but lack even the most basic scientific standards. Even within forensic disciplines that are more firmly grounded in science, evidence is often made to sound more precise than it should. For example, analysts will testify that hairs from a crime scene “match” or “are consistent with” defendants’ hair – but because scientific research on validity and reliability of hair analysis is lacking, they have no way of knowing how rare these similarities are, so there is no way to know how meaningful this evidence is.

Improper Forensic Testimony

Too often, forensic analysts’ testimony goes further than the science allows. Many forensic techniques that have been practiced for years – without the benefit of sufficient scientific research – are accepted and repeated as fact. Juries are left with the impression that the evidence is more scientific than it is, and the potential for wrongful convictions increases.

Improper forensic testimony is not limited to unvalidated disciplines, however. Among the DNA exoneration cases, scores of people were wrongfully convicted after forensic testimony misrepresented serology results. Serology is still used, but before DNA testing it was the only way to help identify the source of blood, semen or other bodily fluids at a crime scene. Using serology, forensic analysts could determine what blood type was present in fluids collected in a rape kit, for example. In many cases, analysts testified properly about what the serology could tell and what percentage of the population shares the perpetrator’s blood type. But in other cases, analysts failed to recognize that the biological sample could be a mixture of fluids from the victim and perpetrator, and the victim’s blood type could mask the perpetrator’s – making it impossible to know the blood type of the perpetrator. In other cases, analysts provide inaccurate statistics for the percentage of the population who share the perpetrator’s blood type.

Forensic Misconduct

The vast majority of forensic science examiners are hardworking, ethical and responsible. They use the best scientific techniques available at the time to deliver objective, solid information – regardless of whether the science favors the defendant, supports the prosecution or is inconclusive.

In many cases, the science – rather than the scientist – is inadequate. In other cases, forensic analysts make mistakes that could result from lack of training, poor support or insufficient resources to meet an ever-growing demand. But in some cases, forensic analysts have engaged in misconduct. While these “bad apples” don’t reflect the entire forensic field, one fraudulent forensic analyst can taint countless cases. For example, in some wrongful convictions later overturned with DNA testing, forensic analysts fabricated test results, reported results when no tests were conducted or concealed parts of test results that were favorable to defendants. In virtually all of these cases, analysts had engaged in misconduct that led to multiple separate wrongful convictions, sometimes in multiple states.

Making Real Reform a Priority

The Innocence Project works at the local, state and federal levels to ensure quality forensic science. Nationally, the Innocence Project supports creating a federal forensic science effort that will stimulate research to validate forensic science disciplines, and will also set and enforce standards. In states, the Innocence Project supports commissions and advisory boards that help make sure forensic facilities have the information and resources they need to do quality work. Meanwhile, the Innocence Project advocates for full funding and enforcement of the existing forensic oversight mechanisms in the Paul Coverdell Forensic Science Improvement Grant Program. This federal program provides critical funding for state and local crime labs and other forensic facilities – on the condition that grant recipients have proper oversight mechanisms in place to handle allegations of serious negligence or misconduct.

Reforms and Solutions

In all of this work, the Innocence Project supports the forensic science field in its efforts to secure the funding it deserves as caseloads grow and demand for forensic testing increases. Crime victims, police, prosecutors and courts all gain from an efficient system that minimizes errors and focuses resources on identifying the guilty. The following recommendations, developed by the Innocence Project during years of research and experience, can substantively address forensic problems and help ensure quality forensic analysis.

Federal Support for Research and National Standards/Enforcement

The Innocence Project believes that a national forensic science effort should focus on three main areas that will most improve the quality of forensics used in the criminal justice system: research; assessment of validity and reliability; and quality assurance, accreditation and certification of laboratories and practitioners. Each area is described below.


A national effort lead by federal science agencies would identify research needs, establish priorities, and design criteria for reviewing forensic disciplines. Funding should also exist for expanded basic and applied research in order to test the validity of extant forensic methods, devices, and assays; and help develop new technologies to solve crime.

Assessment of Validity and Reliability

This federal science coalition would also be responsible for reviewing both existing and new research data to determine whether a technique, device or assay is scientifically valid and reliable for use in casework, and what the parameters of the assay should include. Furthermore, the agency should ensure the discontinuation of any methods that cannot be scientifically supported, and support others only to the extent to which practitioners present and interpret data within scientifically acceptable parameters.

Quality Assurance, Accreditation and Certification

A national forensic science capacity should be created to set and oversee enforcement of standards for public and private laboratories, as well as for individuals conducting forensic tests and examinations with intended use in U.S. federal and state courts. Quality controls and quality assurance programs must create a culture of transparency, implement mechanisms to improve quality management through understanding root causes and secure the integrity of the ultimate forensic product in the laboratory and in the courthouse. Forensic oversight should be obligatory, and non-compliance with accreditation and certification should allow for a loss of accreditation or individual certification and a cessation of business.

State Oversight Commissions or Advisory Boards

Independent panels should be created in each state to help secure adequate resources for forensic work. These independent panels should include a wide range of experts who understand the needs of the forensic community and the criminal justice system alike. Several states have already created commissions or advisory boards; they vary in many ways, but they are independent, expert panels committed to ensuring quality forensics.

Enforcement of Existing Requirements

Every state is eligible to receive federal grant money under the Paul Coverdell Forensic Science Improvement Grant program. The 2004 Justice for All Act, which was passed by Congress and signed into law by President Bush, says states must have oversight mechanisms in place if they receive federal money for their crime labs. Specifically, the law requires jurisdictions seeking federal funding for their forensic facilities to identify an independent, external government entity with an appropriate process to conduct investigations into allegations of negligence or misconduct affecting forensic results. The U.S. Department of Justice’s Office of Justice Programs administers the grants, can improve the information and guidance they need to comply with the oversight requirement. As a result, a number of states lack the independence and/or process necessary to ensure the integrity of analysis from crime labs and other forensic facilities. Many states have accepted the grants but have not fully complied with this requirement.

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