Officers want just as badly to solve the case and may unintentionally provide suggestive clues about the suspect’s identity—a phenomenon known as the “expectancy effect.” Beginning a lineup with comments like “We got the guy and just need you to pick him out,” for example, can prompt an otherwise hesitant witness to hazard a guess.
If a witness has previously seen someone—in an earlier photo lineup, for example, or on social media—they might incorrectly believe they remember that person as the perpetrator. For this reason, the report’s authors recommend against including the same person in successive identification procedures, and urge law enforcement to discourage witnesses from doing their own amateur detective work online.
Police sketches, another staple of criminal procedurals, are another potential source of error. Research shows that people “typically process faces holistically, not feature-by-feature,” which means that a composite cobbled together from a witness’s description of individual features may end up looking nothing like the perpetrator. Yet police, with little else to go on, are likely to start looking for people who look like the composite—straying further away from the witness’s actual description, and perhaps ignoring promising leads in the process.
For the witness, the composite immediately becomes the most tangible representation of someone they may have only briefly glimpsed. During subsequent identification attempts, they may focus on a person’s resemblance to the sketch, as opposed to their recollections of the perpetrator. Because composite or sketch evidence is involved in about a quarter of DNA exonerations, the report authors recommend that law enforcement “only use them rarely and with great caution.”
Courts have long been at least somewhat aware of the shortcomings of these identification procedures. Whether police show a suspect in a photo array or alone, “it is obvious that risks of suggestion attend either form of confrontation,” Supreme Court Justice William Brennan wrote in United States v. Wade.
And as Brennan noted in a different case, Watkins v. Sowders, it is difficult for jurors—impassive observers with no firsthand knowledge of what took place—to be skeptical of an earnest witness who saw a crime with their own eyes and swears to tell the truth in court. Quoting renowned psychology professor and memory expert Elizabeth Loftus, Justice Brennan wrote that “all the evidence points rather strikingly to the conclusion that there is almost nothing more convincing than a live human being who takes the stand, points a finger at the defendant, and says ‘That’s the one!’”
By the time jurors file into the courtroom, though, it is far too late to warn them about all the different mistakes that can occur along the way. At that point, a suspect is an indicted defendant, and after confirming and reconfirming that the defendant is the responsible party, the witness has grown comfortable repeating this narrative to others. As a result, they may have formed a “memory” that never took place.
There are simple strategies available to law enforcement for minimizing the risks of these errors, and the report goes through them in detail: For example, whenever possible, police should conduct double-blind lineups and photo arrays, where neither the witness nor the officer administering the procedure knows who the suspect is. If double-blind procedures are impractical—for example, in smaller departments where everyone knows the suspect’s identity—officers can at least use “blinded” techniques, in which the officer cannot see which suspect or suspects the witness is viewing at any given moment.
So-called filler lineup participants—the people asked to stand next to a suspect in a lineup—should match the elements of the witness’s description of the perpetrator, and not merely look similar to the suspect. The authors also caution against giving witnesses books of mugshots to browse, a practice that may result in witnesses over-committing to their initial identification and being less reliable during subsequent attempts. In 2001, New Jersey Attorney General John Farmer ordered law enforcement agencies to do away with “mugshot-searching” altogether and instead present witnesses with sequential, one-at-a-time lineups. The move, prompted by a U.S. Department of Justice report published two years earlier, made New Jersey the first state to embrace such a shift based on the evolving understanding of memory science.
Using standardized instructions can reduce the likelihood of tainting the proceedings, too. The report suggests that police issue a series of caveats and reminders before each identification attempt: that the suspect “may or may not be present,” for example, and that “it is just as important to free innocent people from suspicion as it is to identify the guilty.” In 2007, lawmakers in North Carolina passed the Eyewitness Identification Reform Act in an effort to modernize identification procedures throughout the state. The act prescribes a set of initial instructions to be given to witnesses, and requires that law enforcement either conduct identifications using independent administrators who are not involved with the case, or use blinding techniques that prevent administrators from knowing whose face the witness is looking at.
Once the witness has made an identification, the report’s authors add, police should take one final, critical step: Immediately ask witnesses for a self-assessment of their confidence, and record it without comment. Detectives should also refrain from giving any sort of suggestive feedback, even after the attempt is ostensibly “complete.” No matter what evidence later comes to light, it can be difficult to convince a witness who saw a detective pump his fist in triumph that the answer they gave was anything other than the right one.
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