How to Avoid Witness Contamination in Suspect Lineups
Impartial eyewitnesses can provide compelling legal testimony of a crime, accident, or other incident they witnessed. But memories are imperfect. Witnesses may forget certain details, such as crucial identifying features of a perpetrator’s appearance. Erroneous information, whether given deliberately or accidentally, can even cause a witness to believe they saw something that wasn’t there. This is known as memory contamination, and it has serious implications in suspect lineups.
What is Eyewitness Testimony?
An eyewitness is a person who sees a legally significant event firsthand. They may later be interviewed by police, asked to identify the perpetrator from a lineup, questioned under oath, and asked to testify in court.
Limitations of Memory
Memories of perceived experiences are not static and may distort, degrade, or evolve over time, especially when misinformation is introduced. For instance, in a 1978 study, subjects watched a slideshow depicting a car hitting a pedestrian. Some subjects were asked leading questions about what happened, such as, “How fast was the car traveling when it passed the yield sign?” when, in fact, the slide depicted a stop sign.
Later, all subjects were shown two slides, one with the original stop sign and another containing a yield sign. The subjects who had been asked about the yield sign during questioning were more likely to pick the incorrect slide. In other words, the leading questions led to an inaccurate memory. This misinformation effect has been demonstrated in hundreds of subsequent studies
Avoiding Witness Contamination in Suspect Lineups
Nearly 70 percent of individuals exonerated by DNA evidence were originally convicted based on eyewitness testimony. The prevalence of mistaken identification underscores the importance of adopting fair lineup procedures.
Consider the problems with a standard lineup:
- The administrator typically knows who the suspect is and may give unintentional cues to the witness about who to pick.
- The witness often assumes the perpetrator must be in the lineup and may select a person despite doubts.
- The administrator may compose a live or photo lineup with non-suspect “fillers” who don’t match the witness’s description, unintentionally causing the suspect to stand out.
- The administrator may not collect a statement from the witness regarding their confidence in identifying the perpetrator.
Here’s how to improve the accuracy of an eyewitness’s memory:
- Conduct double-blind lineups where neither the administrator nor the witness knows who the suspect is.
- Provide instructions that say, “The suspect may or may not be present in the lineup.”
- Compose the lineup so the suspect doesn’t stand out from the fillers.
- Ask the witness to state how confident they feel with their selection.
- Electronically record the lineup procedure for later review.
Many practices that allow eyewitness memories to become contaminated remain widely used today. Fortunately, California is one of 25 states that have implemented the core lineup reforms outlined above.
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