What You'll Learn
The Concept
Witnesses often provide information unavailable from any physical evidence. A witness may describe the offender, a vehicle, words spoken, sequence of events, direction of travel, weapons, clothing, relationships, or conduct before and after a crime. But memory must be understood scientifically. Human memory is not a video file retrieved intact from the brain. Memory involves encoding, storage, and retrieval — and each stage can be affected by environmental and psychological conditions.
A person must first perceive information. Attention may be limited by stress, darkness, distance, divided attention, brief exposure, unexpected events, or focus on a weapon or threat. If information was never effectively encoded, no interviewing technique can perfectly reconstruct it later.
Memories can change after an event. Witnesses may be exposed to media reports, conversations with other witnesses, police questions, photographs, social media, rumors, or repeated retelling. New information can become integrated with original memory — a process called memory contamination.
The way questions are asked can influence what witnesses report. Leading questions may insert information or encourage a desired response. NIJ-supported research has examined how leading and misleading questions affect eyewitness reporting and how alternative interview methods can improve recall.
The cognitive interview was developed using principles from memory research to help witnesses retrieve more information without relying primarily upon suggestive questioning. Early NIJ-supported experiments compared cognitive interviewing methods with traditional approaches and examined their ability to improve witness recall. Cognitive interviewing emphasizes building rapport, allowing uninterrupted narrative, encouraging detailed mental reinstatement of context, using open-ended prompts, avoiding unnecessary interruption, and carefully probing information already provided. The investigator's objective should not be to extract the answer expected — it should be to maximize accurate retrieval.
Identification procedures create additional concerns. Investigators must consider whether fillers are appropriate, whether instructions imply that the perpetrator must be present, whether administrators inadvertently signal a preferred choice, whether confidence is documented promptly, and whether repeated exposure to a suspect affects memory. NIJ has maintained extensive research and training resources concerning eyewitness identification practices.
Confidence deserves careful interpretation. A confident witness can be correct. A confident witness can also be mistaken. Confidence can also evolve after feedback or repeated exposure. The most probative confidence information may therefore be what is documented at the time of the initial identification under appropriately controlled conditions, rather than confidence expressed months or years later.
Eyewitness evidence should generally be treated as evidence requiring preservation, documentation, corroboration, and quality control. The existence of an eyewitness should strengthen an investigation when reliable. It should not terminate critical inquiry.
Real-World Application
A robbery victim is interviewed two days after the crime. The investigator begins with open-ended questions: 'Tell me everything you remember about what happened.' After the victim's narrative, the investigator uses specific but non-leading prompts to explore details. When the victim mentions the suspect's jacket, the investigator asks 'Can you describe the jacket?' rather than 'Was it a red jacket?' This approach — allowing the witness to generate information rather than confirm suggestions — is more likely to produce reliable evidence and less likely to contaminate the witness's memory before a lineup.
Why It Matters
For Police Officers
Investigative interviews are among the most important evidence-gathering activities in any case. Officers who understand memory science can conduct interviews that produce more reliable information and are less likely to be challenged in court.
For Students
Eyewitness science has directly influenced criminal justice policy, from lineup procedures to recording requirements. Students who understand the research can evaluate reform proposals and understand why seemingly confident witnesses can be mistaken.
Think About It
How should juries evaluate confident eyewitnesses who may be sincerely mistaken?
Should all identification procedures be electronically recorded?
How can investigators prevent co-witness contamination when multiple witnesses are present?
What constitutes an appropriately neutral lineup, and who should administer it?
Sources & Further Reading
National Institute of Justice. Eyewitness identification research and training resources. nij.gov.
National Institute of Justice. Research on leading and misleading questions in eyewitness interviews. nij.gov.
National Institute of Justice. Cognitive interview research. nij.gov.
Wells, G. L., & Olson, E. A. (2003). Eyewitness testimony. Annual Review of Psychology, 54, 277–295.