What Makes a Police Lineup Fair?

A police lineup is fair when the suspect does not stand out. That means the fillers, the known-innocent people included alongside the suspect, should match the witness's description of the perpetrator closely enough that a person with no knowledge of the crime could not pick the suspect simply by process of elimination. The witness should be told that the perpetrator may not be present, the administrator should not know which person is the suspect, and the witness's confidence should be recorded at the moment of any identification. These are not bureaucratic niceties. Each one directly affects the risk of a mistaken identification, and mistaken eyewitness identifications have been the most common contributing factor in wrongful convictions later overturned by DNA evidence.

Key takeaways

• A fair lineup requires fillers who match the witness's description so the suspect does not stand out.
• The witness must be told the perpetrator may not be in the lineup; omitting this instruction increases false identifications.
• The administrator should not know which person is the suspect, to prevent unintentional cueing.
• Confidence should be recorded at the moment of identification, before any feedback.
• Unfair lineups do not just risk wrongful convictions; they also weaken the case against a genuinely guilty suspect.

Why does filler selection matter?

The purpose of fillers is to test the witness's memory rather than their ability to spot the odd one out. If a suspect is the only person in the lineup who matches the description, say, the only one with a shaved head or the only one in the right age range, even a witness with a weak memory will tend to choose them. The identification then tells you nothing about whether the witness actually recognises the suspect's face.

Research examined by the National Research Council's 2014 report on eyewitness identification confirmed that lineup composition directly affects both the rate of identifications and the proportion of those identifications that are correct. When fillers do not match the description well, witnesses are more willing to choose the suspect regardless of whether the suspect is the actual perpetrator. The result is a higher rate of identifications overall, but a lower proportion of accurate ones.

The standard approach is to select fillers who fit the verbal description the witness gave, for example "white male, early thirties, brown hair, medium build," rather than people who look exactly like the suspect. Description-matched fillers ensure the suspect does not stand out, while still allowing a witness with a genuine memory of the perpetrator's face to make a correct identification.

What should witnesses be told?

One of the most important safeguards is a simple instruction: the perpetrator may or may not be present in the lineup. Research has consistently shown that when this instruction is omitted, witnesses treat the lineup as a forced choice, assuming the perpetrator must be there and selecting the person who looks most like their memory. This dramatically increases the rate of false identifications, particularly when the real perpetrator is not in the lineup.

The instruction reduces the pressure to choose and makes it more acceptable for the witness to say "I don't see the person." That does not reduce the rate of correct identifications, where the perpetrator is actually present, by much, but it substantially reduces the rate of mistaken ones.

Why does double-blind administration matter?

A lineup administrator who knows which person is the suspect can influence the witness, even unintentionally. Subtle cues, a pause, a glance, a slight change in tone, can steer the witness towards the suspect. After an identification, confirming feedback such as "good, you picked the right person" can inflate the witness's confidence, making a tentative choice feel like a certain one by the time it reaches the courtroom.

Double-blind administration, where neither the witness nor the administrator knows which lineup member is the suspect, removes this risk. It is recommended by the National Research Council, the American Psychology-Law Society and numerous police reform guidelines. The principle is simple: if the administrator does not know who the suspect is, they cannot steer the witness towards them, and they cannot provide meaningful feedback.

Should confidence be recorded?

Yes, and the timing matters. Research by Wixted and Wells found that a witness's confidence at the moment of first identification, under fair conditions, has some value as an indicator of accuracy. But confidence is fragile. It can be inflated by feedback, by repeated questioning, by conversation with other witnesses, and simply by the passage of time and retelling. A witness who said "I think it might be number three" at the lineup may say "I'm absolutely certain it was number three" by the time they testify months later, as explored in can a confident eyewitness be wrong?.

Recording a confidence statement in the witness's own words at the moment of identification captures this information before it can be distorted. It provides a baseline that courts and investigators can use to assess how much the witness's certainty has changed.

What is the difference between a simultaneous and sequential lineup?

In a simultaneous lineup, the witness sees all members at once and compares them. In a sequential lineup, the witness sees them one at a time and makes a yes-or-no decision for each before seeing the next. The sequential approach was proposed to discourage relative judgement, the process of picking whoever looks most like the perpetrator rather than recognising the actual person.

Research on the two formats has produced complex results. Sequential lineups tend to reduce false identifications but may also slightly reduce correct ones. The overall balance of evidence suggests both can work well if other safeguards are in place: proper fillers, an unbiased instruction and blind administration. The format matters less than whether the lineup was constructed and administered fairly.

What makes a lineup unfair?

Common problems include:

• The suspect stands out. Only one person matches the description, or the suspect's photograph is a different size, quality or background from the others.
• No "may not be present" instruction. The witness assumes they must choose, turning the lineup into a guessing task.
• The administrator knows who the suspect is and can, intentionally or not, guide the witness.
• Feedback is given. Telling the witness they chose correctly inflates confidence and alters their memory of how certain they were.
• Multiple viewings. Showing the witness the same lineup repeatedly, or multiple lineups containing the same suspect, increases the chance of a misidentification through familiarity rather than genuine recognition.

Each of these problems is avoidable, which is why the National Research Council and the Innocence Project have emphasised procedural reform as one of the most practical steps for reducing wrongful convictions.

How does Murder Book put players in the position of weighing identification evidence?

Murder Book: The Art of Interrogation is an upcoming narrative interrogation game from Gungrounds, an independent studio in Zagreb, Croatia. It asks players to weigh statements and evidence, including whether the process that produced the evidence was sound. The game is inspired by real police footage and psychological interviews, and it invites players to notice when certainty outruns the quality of the evidence supporting it.

That reflects the research on lineups: a confident identification is only as strong as the procedure that produced it. Cases are designed for focused 5–10-minute sessions. Murder Book is in development for PC (Steam) and mobile, with release currently planned for the end of Q2 2027.

Sources

1. National Research Council (2014), Identifying the Culprit: Assessing Eyewitness Identification. National Academies Press
2. Wells and Olson (2003), Eyewitness testimony. Annual Review of Psychology
3. Wixted and Wells (2017), The relationship between eyewitness confidence and identification accuracy: a new synthesis. Psychological Science in the Public Interest
4. Innocence Project, Reevaluating Lineups: Why witnesses make mistakes and how to reduce the chance of a misidentification
5. Innocence Project, How eyewitness misidentification can send innocent people to prison
6. Gungrounds, Murder Book fact sheet