The need for double-blind methods in police lineups

One of the methods that police use to identify people they suspect may have committed a crime is to put them in a lineup with other people and have eyewitnesses pick them out. But Laura Smalarz writes that the way this is often done is fraught with problems.

On the strength of six eyewitnesses’ lineup identifications, Lydell Grant was sentenced to life in prison in 2012 for the murder of a young Texas man, Aaron Scheerhoorn, who was stabbed to death outside a Houston nightclub in 2010.

All six of those eyewitnesses were wrong.

Thanks to the work of the Innocence Project of Texas, new DNA testing on biological material collected from underneath the victim’s fingernails cleared Grant and implicated another man, Jermarico Carter, who police said confessed to the killing. Carter has now been indicted for the murder by a grand jury, and Lydell Grant was released from prison.

But faith in eyewitnesses runs so deep that despite the overwhelming proof of Grant’s innocence, the Texas Court of Criminal Appeals initially refused his exoneration request. Instead, they asked that the six eyewitnesses who originally testified against Grant respond to his claims of innocence. Finally, almost a year later, the Texas Court of Criminal Appeals declared Grant “actually innocent” on May 19, 2021.

So how is that six people misidentified him? The answer is that because the people conducting the lineup had suspicions about him, they gave cues that influenced the witnesses.

The transcript from Lydell Grant’s trial revealed that the homicide detective in charge of investigating the case administered the lineup to the eyewitnesses. Of course, he knew that Lydell Grant was the one under suspicion.

Psychological experiments have shown that lineup administrators who know who the suspect is end up cuing witnesses toward that person. Compared to administrators conducting double-blind lineups, these informed administrators are more likely to ask witnesses about the suspect and smile when witnesses are looking at the suspect rather than at another person in the lineup.

Such behaviors are often inadvertent; neither lineup administrators nor eyewitnesses may be consciously aware that they’re happening. Nevertheless, these subtle behavioral cues affect eyewitnesses’ decisions by making them more likely to choose the suspect.

But if the six eyewitnesses chose Lydell Grant from the lineup only because they were cued to do so by the case detective, why were they so confident in their identifications? According to the trial transcript, most of the eyewitnesses testified to having been positive when they picked Grant out of the lineup. One reported that he had identified Grant without doubt or hesitation. Another stated that the killer’s face was “burned into [her] memory immediately.”

The witnesses’ trial testimony reveals a simple explanation for these high-confidence errors: All of the eyewitnesses received confirmatory feedback following their identification of Grant.

Some of you may remember the story of Clever Hans, the horse that could carry out simple arithmetic problems. This caused a sensation until it was found that the horse picked up on subtle cues from its trainer who was unaware that he was providing the cues.

The solution to the eyewitness problem is clear: double-blind testing

Scientific best practices for conducting eyewitness lineups require that the person administering the lineup not know who the police suspect. Just as double-blind clinical trials in medical studies are intended to prevent patients’ and doctors’ expectations from affecting outcomes of the clinical trial, double-blind lineups aim to prevent witnesses’ and administrators’ expectations from influencing the outcomes of the identification procedure.

In addition to implementing double-blind lineup procedures, it’s essential that lineup administrators document eyewitnesses’ confidence immediately following an identification. Confidence collected at the time of an identification during a double-blind lineup procedure is informative regarding the eyewitness’s accuracy. Confidence reported at trial after the eyewitness has received confirmatory feedback is not.

The problem as always is that very often, the desire of the police and prosecutors to get a conviction and close the case overrides the desire for justice, even if the price paid is that innocent people spend years in prison and even get executed.


  1. kestrel says

    Ha! The minute I started to read this story I immediately thought of Clever Hans.

    We have a neighbor convinced that dousing is real, because someone came to their house and did some dousing, and found the *exact spot* that the owner thought was where there was water. Of course, the owner was standing right there as the douser performed their magic trick. Gee, I wonder how the dowser managed to pick out that exact spot…

  2. Matt G says

    This seems very fair and reasonable. The police will hate it. Anything that challenges their authority….

  3. jrkrideau says

    @ 1 kestrel
    The minute I started to read this story I immediately thought of Clever Hans.

    Same here. It’s glaringly obvious.

    Unfortunately, judges and juries tend to believe eyewitnesses and confessions even if the evidence is fairly clear that both are very dubious.

    Of course, most forensic “sciences” seems more sciencey than scientific. And that does not begin to cover the grifters selling all sorts of woo or the complete misuse of valid methods and tools.

    Work by people like Elizabeth Loftus on false memories or Linda Shaw’s on false confessions does not reassure me about police techniques.

  4. Holms says

    Thanks to the power of confabulation, it is very possible that the people genuinely do believe that face to be the face of the killer, after having had it reinforced to them in the lineup process.

  5. John Morales says

    Line-ups can never be double-blind; at least, not if the suspect is known to be part of it.

    Specifically, the very point of a line-up is predicated on the purported perpetrator being part of it.


    Thanks to the power of confabulation, it is very possible that the people genuinely do believe that face to be the face of the killer

    Nah. It remains “very” possible (heh) regardless of confabulation, so its power need not be thanked.

  6. lanir says

    I wonder… As we get more and more people who are proved innocent in situations like this and we know it can be difficult to get started with life again after being in prison for some time, maybe the solution to two problems is to have them solve themselves? If prosecutors get to have the same forensic scientists present evidence at hundreds of trials for a fee maybe a similar opportunity could be presented to exonerated prisoners?

  7. ardipithecus says

    Erle Stanley Gardner, who was a successful criminal lawyer before his writing career, wrote essays described the same problem, in pretty much the same terms, back in the 1930’s. It’s not going to change until enough people want it to change, which is not in the foreseeable future.

  8. jrkrideau says

    @ 5 John Morales
    Line-ups can never be double-blind
    I am not sure as it may depend on how you define “double blind” but the presiding officer seems to be the only one who should be blinded. Or not even present.

  9. Bruce says

    The prosecutor should be indicted as being a co-conspirator with Carter, after the fact, because the prosecutor acted to cover for Carter by railroading someone else. Only if prosecutors see their own prosecution as likely will they change. Unfortunately, the law doesn’t allow thus.

  10. GerrardOfTitanServer says

    Line-ups can never be double-blind; at least, not if the suspect is known to be part of it.

    You could also roll dice for a 50-50 chance that each lineup actually contains the suspect. I haven’t thought this through fully, but something like this should be workable.

Leave a Reply

Your email address will not be published. Required fields are marked *