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Contributing Factors

Wrongful convictions rarely have only one type of contributing factor. More often, wrongful convictions come from a tangled combination of errors that stem from flaws in the proper use of science, lack of protective measures in the criminal legal system, and weaknesses in human behavior and psychology. This list highlights the most prevalent contributing factors in wrongful conviction cases.

Eyewitness Misidentification


In cases without DNA evidence, eyewitness identifications are often the most relied-upon form of evidence. Eyewitness testimony can be highly persuasive for a jury, but it can also be highly inaccurate. Problems with eyewitness identifications can come from the conditions of the crime scene: an incident may occur very quickly, in the dark, or when the perpetrator is not fully visible. Stress and fear also contribute to fuzzy or inaccurate memories of an incident, particularly when the perpetrator had a weapon (known as “weapon focus”). 

Problems can also arise from the circumstances surrounding identification procedures: if the police have an idea of a suspect, they may—purposefully or accidentally—pressure a witness to identify the preferred suspect. Further, if a witness is also a victim, they may fear that the investigation will stop if they do not identify a suspect and therefore feel pressured to select the “best match” relative to the options. 

Additionally, research suggests that cross-racial identifications have a higher rate of inaccuracy. This means that when people attempt to make an identification outside of their own race, they are more likely to get that identification wrong. 


In 2020, the American Psychological Association made the following recommendations to reduce the rate of eyewitness misidentification: 

PRE-LINEUP INTERVIEWS – before conducting an identification procedure, an officer should document a witness’s description of the incident, suspect, and conditions in their own words, and warn them not to confer with other witnesses during the investigation. 

EVIDENCE-BASED SUSPICION – officers should not include a potential suspect in a lineup unless there are separate, evidence-based grounds to suspect that person as the culprit. 

DOUBLE-BLIND ADMINISTRATION – lineups should be conducted so that both the witness and the administrator do not know who the suspect is in the lineup.

LINEUP FILLERS – fillers (other photos or people in the lineup who are not suspects) should not make the suspect stand out as distinct from the group, based on clothing, background, or general physical appearance. 

PRE-LINEUP INSTRUCTIONS – before the identification procedure, the witness should be told that the lineup administrator does not know who the suspect is; that the culprit might not be in the lineup at all; that they are allowed to indicate that they do not know or that none of the photos resemble the culprit; that they should be prepared to state how confident they are in their choice; and that the investigation will continue even if they do not make an identification. 

IMMEDIATE CONFIDENCE STATEMENT – after making an identification or being unable to make an identification, the witness should make a statement about how confident they are in their choice. 

VIDEO-RECORDING OF THE WITNESS – the entire process—before, during, and after identification—should be recorded. 

AVOID REPEATED IDENTIFICATIONS – officers should not repeat an identification procedure with the same suspect and witness. 

SHOW-UPS – show-ups (when only one suspect is shown to a witness during an identification procedure) should be avoided whenever lineups are possible. 

False Confessions


When asked, most people might assume that they would never confess to a crime that they did not commit. The pressures, fear, and isolation of the criminal legal system make this unimaginable situation rather common: according to the National Registry of Exonerations, about 12% of known wrongful convictions involve a false confession. 

A person may falsely confess because of coercive techniques used by law enforcement. In extreme situations, law enforcement may resort to physical abuse to extract a confession. More often, false confessions involve emotional and psychological manipulation. Interrogation techniques commonly used by police officers promote accusatory strategies designed to move a suspect closer to a confession. 

Under such methods, officers are trained not to accept innocence claims from suspects. An officer might minimize the seriousness of a crime or promise leniency to make a confession easier for the suspect. An officer might also lie to a suspect about evidence that exists against them, to make them feel trapped. 

Law enforcement might also—intentionally or not—take advantage of a suspect’s vulnerabilities, including stress, fatigue, age, or disability, to elicit a confession.


Law enforcement should use alternative methods of interrogation that involve open-ended questioning and being an active listener, which put an emphasis on getting a suspect’s story and not simply a confession. Interrogations should also be limited in time and recorded on video to ensure that officers follow proper protocol and do not overwhelm a suspect into giving a confession. 

A confession should not be admitted as evidence when the suspect had certain qualities that made them uniquely susceptible to false confessions: this includes extremely young suspects or those with special needs or disabilities. 

Source: University of Cincinnati Law Review

False or Misleading Forensic Evidence


Two fundamental tenets of good science are validity and reliability. Validity refers to how accurately the evidence reflects truth and reality; reliability refers to how consistent scientific results are when the same methods are applied. Forensic science in the United States often lacks both validity and reliability, making it a leading cause of wrongful convictions. 

The National Academy of Sciences released a report in 2009 that extensively detailed problems with forensic science in the United States and made recommendations for reform. The NAS report noted the following problems: 

  • disparities in the operation and application of forensics across different jurisdictions and law enforcement agencies; 
  • lack of mandatory standardization, certification, or accreditation processes; 
  • large disparities in funding across jurisdictions, and lack of sufficient funding; 
  • unclear and overly broad range of “forensic science” disciplines, including who qualifies as an “expert”; 
  • insufficient and inconsistent protocols for interpreting forensic science results.

The President’s Council of Advisors on Science and Technology (PCAST) released a report in September 2016 as a follow-up to the NAS report and focused on problems in “feature-comparison” forensic methods. Forensic analysists use feature-comparison when they are comparing evidence samples, looking for a “match”—this often occurs with bite marks, fingerprints, ballistics, footprints, and hair. The PCAST report found a lack of validity and reliability in the application of feature-comparison methods, which lack consistent standards. 

A key problem with the validity and reliability of forensic evidence is the way analysts sometimes deal with inconclusive or uncertain results. At times, expert witnesses may testify to exaggerated statistics, like “one in a million,” that do not have actual scientific support. These hyperbolic reports—along with forensic science’s highly inaccurate depictions on television—often make forensic science results seem far more conclusive than they are. Recent studies suggest that forensic analysts are vulnerable to confirmation bias when they know the suspect or the crime theory that police have in mind, and they feel pressure to make the evidence fit law enforcement’s theory. Confirmation bias undermines the scientific method: instead of crafting an experiment or test to determine what conclusions are supported, forensic analysts might start with a conclusion and craft a test to reach it.

Expert testimony is highly persuasive to juries and judges; when other courtroom parties do not have a background in science, they commonly take experts at their word. 


The National Academy of Forensic Science made thirteen recommendations for reform in its 2009 report, centering on the creation of an independent forensic science oversight body to ensure validity and reliability, and the creation of techniques to address cognitive bias in forensic analysts, attorneys, and judges. Many of the NAS’s recommendations have not been applied to their full extent; extensive reform is still needed to improve forensic science.

The President’s Council of Advisors on Science and Technology made recommendations directed at the National Institutes of Standards and Technology, the White House Office of Science and Technology Policy, the FBI Laboratory, the U.S. Attorney General, and the judiciary generally. The recommendations centered on these federal agencies taking the lead on studying the validity of new forensic science methods, creating objective standards for all jurisdictions, creating standards for expert testimony to ensure accuracy in the courtroom, and educating judges on how to consider proper scientific criteria when evaluating the admissibility of expert testimony. 

Reform measures should include the use of multiple comparison samples and blind replication of results for comparison. Additionally, analysts and scientists should not have access to multiple lines of evidence from which to draw conclusions; they should only have access to what they must be examining. 

States must also enact laws that provide a mechanism for wrongfully convicted people to get back into court to prove their innocence in cases where forensic or medical evidence used to convict them has subsequently been undermined or discredited by scientific advancements. Some states, such as Texas, have passed “junk science” laws, which allow incarcerated people to challenge their convictions on the basis of questionable “scientific” evidence being used against them. 

Sources: New York Times; Forensic Science International; Royal Statistical SocietyThe Innocence ProjectThe White House Archives.

Official Misconduct


Official misconduct typically includes actions taken by police and prosecutors, though it can refer to any misconduct by an official member of the criminal legal system. Official misconduct falls into five general categories: witness tampering; misconduct in interrogations; fabricating evidence; concealing exculpatory evidence (also known as a Brady violation); and misconduct at trial (e.g., officer perjury).

Official misconduct is a leading cause of wrongful convictions that have led to exonerations; a 2020 study by the National Registry of Exonerations found official misconduct in 54% of these cases. That rate increases for more serious and severe crimes.

According to the National Registry of Exonerations, “Black exonerees were slightly more likely than whites to have been victims of misconduct (57% to 52%), but this gap is much larger among exonerations for murder (78% to 64%)—especially those with death sentences (87% to 68%)—and for drug crimes (47% to 22%).

Brady violations tend to be the most common form of misconduct, and the National Registry of Exonerations has found concealed exculpatory evidence in 44% of exoneration cases. 


Official misconduct can be reduced and ultimately prevented. Reforms should include better-defined procedural and evidence-gathering rules, with real enforcement mechanisms to ensure that the rules are followed. Accountability can be promoted through immediate and regular discipline for infractions. 

Misconduct often finds its roots in leadership: therefore, electing local prosecutors, sheriffs and other law enforcement leaders who will create an honest, transparent, and accountable work culture can reduce the incidence of misconduct. 

Prosecutors have extraordinary power in the criminal legal system: they can help to prevent misconduct by dropping cases where misconduct has occurred, making a commitment to prosecute law enforcement actors who obstruct justice, and reexamining past cases when there is evidence of innocence.

Source: National Registry of Exonerations.

Perjury, False Accusations, and Informant Testimony


Perjury occurs when a witness provides false testimony in a court of law. The National Registry of Exonerations has found perjury and false accusations in 57% of exoneration cases. Perjury and false accusations often occur when a witness has an incentive to lie, including ill-will toward the accused, the desire to please law enforcement, or the desire to deflect suspicion (such as a co-defendant accusing another of the whole crime, or arguing that they were coerced). This kind of inaccurate testimony can come from people involved in the case, uninvolved in the case but known to the accused, or complete strangers. 

Informants unknown to the accused might offer false testimony in order to receive favorable treatment from prosecutors and police. Also known as “jailhouse snitches,” wrongful conviction cases can involve the testimony of informants who are facing their own involvement with the legal system, and often who are already incarcerated. These informants may receive leniency, or the simple promise of leniency, in their own cases if they agree to testify in another case. Typically, their testimony centers on the accused “confessing” the crime to them while the two were in jail together. This practice incentivizes informants to perjure themselves—in other words, to give untruthful testimony on the stand—in order to help the prosecutor’s case and receive their own benefits. Nearly one-fifth of DNA exoneration cases have involved informant testimony. 


Perjury by informants can be prevented by limiting informant testimony as well as prosecutors’ ability to use incentivized testimony. Pre-trial hearings to assess the reliability of such witnesses, and jury instructions that instruct jurors to consider the incentives when evaluating an informant’s testimony, can help to restrict these issues. 

Because the same informants are often seen across many cases, local jurisdictions should also begin to keep track of the use of jailhouse witness testimony and the individuals who frequently appear in court. 

Jurisdictions should strengthen discovery laws to ensure that a defendant has access to information about a witness’s incentive and credibility before trial. Legislatures and the judiciary should also create rules on corroboration of testimony, to prevent convictions based on a single witness who lacks credibility. 

Source: The Innocence Project