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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