Skip to main content

Verified by Psychology Today


Protecting the Innocent: Lineups, Good and Bad

The psychology of law enforcement lineups is crucial for accurate identification

Key points

  • Valid lineups in law enforcement are crucial in criminal identification and in judgments of guilt or innocence.
  • However, the context of a lineup, and even the behavior of the investigator, can bias the results of a lineup identification.
  • The psychology of lineup administration can prove critically important for successful, valid identifications.
Matthew Sharps
Matthew Sharps

In previous posts of the Forensic View, we've seen the difficulties inherent in the Field Identification Procedure (FIP) or "show-up." A superior method of suspect identification is to be had in the law enforcement lineup.

Lineups are familiar to everyone, from myriad detective shows and movies. Yet lineups are frequently poorly understood. For example, contrary to police comedies, live lineups, with several individuals (typically from a jail population) literally lined up with a suspect for a given witness, are rare in actual investigations.

More typically, lineups are conducted with head-and-shoulder photographs from booking procedures. In such lineups, a photograph of a suspect is displayed to a witness, together with several “foils,” pictures of similar individuals. The witness is, of course, supposed to choose the suspect. Lineups can also be administered without the actual suspect's photo being present in order to control for the prospect of “false positives"; however, this ideal is seldom met in real‐world police work. Even so, the witness is at least to be admonished that the suspect may or may not be among the alternatives (USDOJ, 1999).

Unlike the field identification procedure, the lineup does not force the witness to a yes/no judgment about an individual suspect. Lineups at least require witnesses to choose among plausible alternatives. This is why, whenever consistent with public and officer safety, the lineup should be used instead of the show-up (USDOJ, 1999).

Yet how accurate are lineups?

For some years, there has been a heated argument between advocates of sequential lineup procedures and believers in more traditional, simultaneous “six‐pack” photo arrays (see Mecklenburg, Bailey, & Larson, 2013). Note that in the United States, a lineup array typically consists of six photographs. In many other nations, that number is increased substantially.

The major methodological difference is that the sequential method requires that the pictures be shown one at a time rather than side‐by‐side. This method is slightly less likely to impugn the innocent. The more traditional, simultaneous method is apparently slightly more likely to impugn the innocent, although also more likely to identify the guilty correctly. Results in this debate are not entirely consistent, and political considerations are sometimes unfortunately involved. The psychological dynamics of these two methods are explored in greater depth elsewhere (Sharps, 2022; see also Mecklenburg et al., 2013). Further research may clarify these issues.

Ultimately, though, there is general agreement that the lineup is superior, in terms of accuracy, to the show-up and should be used instead whenever circumstances permit.

However, lineups have to be used correctly.

Human beings are very good at reading the facial features of other human beings. A classroom demonstration I have used many times: standing at a student's desk, if I look at a given photograph in a simultaneous lineup on that desk, the student can immediately tell which photo claims my attention.

Every time.

Although the investigator would be best unaware of the true identity of the suspect, in the recommended "double-blind" procedure (USDOJ, 1999), in practice, this is seldom the case. Obviously, the investigator's attention will be on the guilty party. Therefore, a witness may not base identification on the memory of the crime. The witness may base it on the direction of the investigator's gaze. This is why it's important for a lineup administrator to stand outside the witness's line of sight when administering a lineup. If the investigator inadvertently looks at the suspect's image, the witness may very well follow suit.

The construction of the lineup also matters, of course. Consider several instances, from my own work as a consulting investigative psychologist, of important issues that could completely derail an otherwise sound criminal case:

1. Make sure that all your foils, and the suspect, are of the same race. If the witness was mugged by a blonde, please don't place a single pale blonde among five photos of dark-complexioned brunettes. You can guess what your witness is going to do.

2. If the reported suspect has a beard, don't have your suspect looking like Santa while everybody else is clean-shaven. Also, if the beard was "full" or "heavy," don’t put the guy who looks like Santa in with five guys with soul patches. Granted, they all have "beards," but you'll lose the case anyway. And don't forget: If you've gotten the wrong suspect and you put him away, the actual perpetrator is still out there. Not what you want.

3. Don’t dress your suspect in a button‐down shirt while everybody else is in a jail uniform, and especially don’t match that shirt to the witness’s description. Your suspect, if present in your lineup, should be visually very similar to your foils.

4-6. Don’t show your suspect’s face in a menacing closeup while everybody else is seen as a tiny head somewhere in the middle of the photo. Don’t photograph your subject against a different color background than everybody else. And for heaven’s sake, don’t pin a large post‐it above the head of your suspect, a glowing goldenrod indicator of guilt, when nobody else has one. Your suspect, if present in your lineup, should be visually very similar to your foils.

In all of these cases, of course, the lineup was biased by the way in which it was constructed. These obvious biases posed a significant credibility problem to the judge and jury, gleefully pointed out by the defense and met with rage and gnashing of teeth by the prosecution. These types of lineup errors have, in fact, rendered specific lineups, legally and practically, effectively useless.

However, the fact remains that a properly conducted police lineup provides very powerful evidence in court. Even with a perfectly conducted lineup, of course, a given identification can be wrong; the paramount importance of good physical evidence cannot be overemphasized. Yet the fact remains that a solid, well‐conducted lineup frequently provides very compelling evidence in court. The investigator's task is to ascertain that the given lineup is fair to all concerned in any given criminal proceeding.


Mecklenburg, S.H., Bailey, P.J., & Larson, M.R. (2013). Eyewitness Identification: An Update on What Chiefs Need to Know. The Police Chief, 80, 60-63.

Sharps, M.J. (2022). Processing Under Pressure: Stress, Memory, and Decision-Making in Law Enforcement (3rd ed.). Park City, Utah: Blue 360 Media.

USDOJ (United States Department of Justice, 1999). Eyewitness Evidence: A Guide for Law Enforcement. National Institute of Justice, Office of Justice Programs.

More from Matthew J. Sharps Ph.D.
More from Psychology Today