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Evidence Issues

Below are examples of common problems and issues with evidence that can lead to wrongful convictions:

Eyewitness Identification

One of the major causes of wrongful convictions has been eyewitness misidentification. Misleading police lineup methods have been used for decades without serious scrutiny.

While eyewitness testimony can be persuasive evidence before a judge or jury, years of strong social science research has proven that eyewitness identification is often unreliable. Misidentifications don’t only threaten the innocent, they also derail investigations.

In October 2014, the National Academy of Sciences (NAS), the nation's premier scientific entity, issued a groundbreaking report, Identifying the Culprit: Assessing Eyewitness Identification, settling many long-debated areas of this police practice and identifying a set of reform procedures. You can find this report on our Wrongful Conviction Project Resources page.


Several easy-to-implement procedures have been proven to significantly decrease the number of misidentifications. However, acceptance of these changes has been slow. The Innocence Project recommends that all jurisdictions immediately adopt the following policies:

  • Blind administration: Research and experience have shown that the risk of misidentification is sharply reduced if the police officer administering a photo or live lineup is not aware of who the suspect is.
  • Lineup composition: “Fillers” (the non-suspects included in a lineup) should resemble the eyewitness’ description of the perpetrator. The suspect should not stand out (for example, he should not be the only member of his race in the lineup, or the only one with facial hair). Eyewitnesses should not view multiple lineups with the same suspect.
  • Instructions: The person viewing a lineup should be told that the perpetrator may not be in the lineup and that the investigation will continue regardless of the lineup result. They should also be told not to look to the administrator for guidance.
  • Confidence statements: Immediately following the lineup procedure, the eyewitness should provide a statement, in his own words, articulating his the level of confidence in the identification.
  • Recording: Identification procedures should be videotaped whenever possible. This protects innocent suspects from any misconduct by the lineup administrator, and helps the prosecution by showing a jury that the procedure was legitimate.
  • Sequential presentation of lineups: Research has shown that presenting lineup members one-by-one (sequential), rather than at once (simultaneous), decreases the rate at which innocent people are identified. Research has also demonstrated that when viewing several subjects at once, witnesses tend to choose the person who looks the most like – but may not actually be – the perpetrator.

False Confessions

For many reasons – including youth, inexperience, intellectual ability, mental health issues, and aggressive law enforcement tactics – innocent people sometimes confess to crimes they did not commit.

While it can be hard to understand why someone would falsely confess to a crime, psychological research has provided some answers, and DNA exonerations have proven that the problem is more widespread than many people think. In more than 25% of the wrongful convictions overturned with DNA evidence, defendants made false confessions, admissions, or statements to law enforcement officials.


The electronic recording of interrogations, from the reading of Miranda rights onward, is the single best reform available to stem the tide of false confessions.

For the recording of interrogations to be effective, the entire custodial interrogation must be recorded. This record will improve the credibility and reliability of authentic confessions, while protecting the rights of innocent suspects.

In some false confession cases, details of the crime are inadvertently communicated to a suspect by police during questioning. Later, when a suspect knows these details, the police take the knowledge as evidence of guilt. Often, threats or promises are made to the suspect off camera and then the camera is turned on for the confession. Without an objective record of the custodial interrogation, it is difficult to gauge the reliability of the confession.

For law enforcement agencies, recording interrogations can prevent disputes about how a suspect was treated, create a clear record of a suspect’s statements, and increase public confidence in the criminal justice system. Recording interrogations can also deter officers from using illegal tactics to secure a confession.

Arson and the Evolution of Fire Science
Recent advances in fire science and the acceptance and reliance on the scientific method have completely dispelled the myths and misconceptions previously relied on by fire investigators.

While fire investigation now is largely a scientific pursuit, in the past, fire investigation was considered by many as more of an art than a science, with investigation techniques and beliefs passed down through apprenticeship rather than scientific or academic study. Conclusions were often reached by observation alone rather than application of the scientific method.

In 1992, the National Fire Protection Association first published NFPA 921: Guide for Fire and Explosion Investigations, which eventually came to be regarded by fire investigators and courts as the standard for fire investigation methodology and interpretation. Over the past two decades, multiple editions of NFPA 921 have been published in an effort to keep up with the continuous scientific advancements in fire investigation.

Studies by the ATF show that even the most experienced fire investigators made grave mistakes, especially in post-flashover fires. Flashover occurs when the fire spreads rapidly to all exposed combustible materials and progresses to full-room involvement.

In 2005, a training exercise was conducted by the ATF in which two identical cells were burned to the point of flashover, and 53 fire investigators were asked to determine in which quadrant of each cell the fire started. For each cell, only three of the 53 investigators correctly identified the quadrant of origin, a rate of 5.7%.

Despite the publication of NFPA 921, progress was slow. General analysis of the fire investigation profession further showed that many investigators continued to treat fire investigation as an art. In 2009, the National Academy of Sciences, in a landmark report addressing several forensic sciences, acknowledged that fire investigators continued to make determinations regarding the intentional setting of a fire using “rules of thumb” that had been discredited. It was recommended that further experimentation was needed “to put arson investigations on a more solid scientific footing.” The National Academy of Sciences Report can be found on our Wrongful Conviction Project Resources page.

The fire investigation paradigm has shifted. In 2013, the International Association of Arson Investigators issued a position statement acknowledging that the National Fire Protection Association, NFPA 921: Guide for Fire & Explosion Investigations is an “authoritative guide for the fire investigation profession.” In recent years, many convictions have been overturned based upon the evolution of fire science.