Cognitive Biases in Criminal Investigations: When Psychology Traps the Truth

In the collective imagination, the ideal investigator embodies scientific rigor and absolute objectivity. Yet even the most experienced professional cannot escape a fundamental reality: they remain a human being, subject to emotions, instincts… and cognitive biases.

A cognitive bias — sometimes called an “unconscious bias” — refers to the distortion that affects information when it is not processed analytically by a person’s cognitive system. This distortion influences the way information is unconsciously interpreted, evaluated, and remembered.

These reasoning errors, often unconscious, shape our decisions without our awareness. In an investigative context, they can subtly divert the search for truth toward a mistaken interpretation, sometimes leading to judicial dead ends. Many cases that remain unsolved today — commonly referred to as cold cases — trace their origins to one of these biases: invisible, yet dangerous.

The Anchoring Bias: Trapped by the First Impression

Anchoring bias is one of the most insidious. It arises at the very moment the investigation begins, when the first piece of information received becomes a reference point around which all subsequent reasoning revolves.

If, in the early hours, a suspect or hypothesis appears plausible, the human mind tends to evaluate everything thereafter through that initial frame. Every new clue is interpreted through that lens, reinforcing the original conviction rather than prompting re‑evaluation.

Consider a concrete example: at a bloody crime scene, a witness mentions having seen a person known in the neighborhood as hot‑tempered and impulsive. From that moment, the investigator’s focus anchors on this individual. During interviews, every nervous tick and expression seems to confirm guilt. The danger is clear: attention drifts away from anything contradicting that first impression.

Thus, a hypothesis born of coincidence or intuition becomes a manufactured truth.

Confirmation Bias or Tunnel Vision: Seeing Only What One Wants to See

Closely related to anchoring, confirmation bias — also known as tunnel vision — drives investigators to seek information that confirms their hypothesis while disregarding what contradicts it.

This psychological mechanism gives the brain a sense of coherence, of mental comfort. Yet that illusion of certainty can be fatal in investigative work, where neutrality is an essential professional standard.

It is arguably the most common cognitive bias in criminal investigations, and unfortunately, it has led to numerous miscarriages of justice over the decades: focusing only on incriminating evidence, reinterpreting witness statements to fit a pre‑existing theory, or dismissing alternative leads as “inconsistent.” Truth becomes partial, truncated by subjective perception.

To counteract this bias, some investigative units now implement external review procedures: an independent colleague re‑examines the case file without prior exposure to the dominant hypotheses, identifying what others may have overlooked.

Likewise, to avoid this cognitive distortion, criminal profilers commonly build their behavioral analyses using the entire file while deliberately excluding any knowledge of the investigators’ suspect list.

The Pendulum Bias: From One Error to Its Opposite Extreme

No investigator is immune to past mistakes. Experience refines judgment, but it can also distort it. The pendulum bias occurs when, in an effort at self‑correction, the human mind swings too far in the opposite direction.

For example, an investigator who was previously too lenient — perhaps releasing a suspect who later proved guilty — may be overly severe in the next case. They scrutinize every microexpression, interpret every inconsistency as evidence of guilt, and fall prey to overzealousness.

This shift, often driven by fear of repeating an error, can create mental rigidity incompatible with objective analysis.

Cognitive balance depends on the ability to learn from mistakes without becoming captive to them. Reflective self‑management and clinical supervision can help investigators maintain the psychological stability essential to sound decision‑making.

Groupthinking: The Consensus That Kills Truth in Criminal Investigation

A criminal investigation is rarely a solitary endeavor. Decisions are often made collectively, within teams where each member plays a complementary role. But this collective dynamic, effective in appearance, hides a major danger: groupthinking.

This bias arises when social or hierarchical cohesion outweighs critical thought. Out of fear of contradicting a superior—or of undermining team unity—investigators align with the dominant opinion even when they detect inconsistencies. The result is an illusion of certainty: if everyone agrees, it must be true.

Major investigative failures documented around the world often share this component. In certain serial murder cases, the collective refusal to consider another hypothesis—such as the possibility of an uncaught offender—delayed identification of the true suspect for years.

Preventing groupthinking depends on organizational culture: encouraging constructive dissent, valuing critical re‑evaluation, and creating spaces where hierarchy temporarily gives way to open discussion.

Mirror Reasoning: Assuming the Other Thinks Like You

Criminal profiling relies on understanding human behavior—but also on recognizing its diversity. Mirror reasoning leads to a form of psychological blindness: investigators project their own logic, moral framework, and motivations onto the suspect they are trying to understand.

This bias is particularly dangerous in cases involving atypical offenders—serial killers, sexual predators, ideological terrorists. Assuming that such individuals “think like everyone else” is to misunderstand their psychological structure, which is often deviant or radically different.

For example, an analyst who assumes a suspect “will eventually confess out of guilt” applies an emotional model irrelevant to a psychopath devoid of remorse or empathy. Likewise, by projecting their personal values, an investigator may underestimate the symbolic or ritualistic elements driving psychologically motivated crimes.

This gap between perception and reality leads to misinterpretation and, in turn, ineffective interrogation or pursuit strategies. A sound profiling process must therefore be rooted in empirical knowledge of offender typologies, not personal projection.

Linkage Blindness: When the Puzzle Remains Incomplete

Less psychological but equally pernicious, linkage blindness refers to the failure to connect multiple crimes committed by the same offender. This phenomenon often results from institutional compartmentalization: differing jurisdictions, poor information‑sharing, incompatible databases, or methodological discrepancies.

At the heart of this structural blindness, however, lies another cognitive bias: not seeing the connection simply because one is not expecting it. Differences in modus operandi, location, or an offender’s behavioral evolution can be enough to conceal the obvious. As a result, each crime is treated in isolation, and the broader pattern emerges only years later — often far too late.

Solutions lie as much in methodology — interlinking databases, conducting systematic behavioral analyses — as in investigative culture: cultivating systemic curiosity, resisting data compartmentalization, and acknowledging that crime evolves over time just as offenders do.

When Biases Feed Cold Cases

Unsolved cases are not always due to lack of evidence. More often, a human misinterpretation prematurely closes off a promising lead: a misjudged witness, a discounted hypothesis, or an uncorrelated trace. Viewed through the lens of bias, these details become missed opportunities.

In reopening unsolved cases, criminal profilers play a crucial role: they re‑examine files through the prism of initial cognitive biases, a standard part of comprehensive case analysis. Understanding where and why thought became fixed can reopen new investigative perspectives. Sometimes, truth re‑emerges only when certain certainties are unlearned.

Conclusion: Restoring the Place of Psychological Rigor

No investigation is entirely objective. But recognizing our biases, understanding them, and implementing cognitive safeguards are essential steps toward a more enlightened justice system.

Scientific rigor does not begin with fingerprints, DNA analyses, or technology—it begins in the mind of the person seeking the truth.

Training investigators in cognitive psychology, instituting external review mechanisms, promoting a culture of intellectual debate within investigative units, and systematically involving a criminal profiler in cases of violent and complex crimes are indispensable strategies.

For in criminal investigation, as in every human pursuit, the greatest threat to truth is not the lie… but certainty.

Némésis offers criminal profiling services, polygraph testing, investigation, and investigative analysis to Quebec police forces, legal professionals, as well as any entity or citizen requiring specialized expertise in investigation.