Case File 313 · Investigation Psychology

How Do Investigators Avoid Falling in Love With One Theory?

By Murder Book Editorial TeamPublished by Gungrounds, the studio making Murder BookPublished 3 October 2026Updated 3 October 2026

Investigators avoid falling in love with one theory by deliberately testing it against alternatives, actively searching for evidence that contradicts it, and building structured safeguards into the investigation process. The core problem is confirmation bias: once a person forms a hypothesis, they naturally tend to seek, notice and remember information that supports it while overlooking information that does not. In criminal investigation, this pattern can harden into tunnel vision, where an entire case is built around a premature conclusion. Research on wrongful convictions consistently identifies this failure as a contributing factor. The solution is not to avoid forming hypotheses, which would be impractical, but to treat every hypothesis as something to be tested rather than defended.

Key takeaways

Confirmation bias is the tendency to seek and interpret evidence in ways that support an existing belief, and it affects everyone, including experienced investigators.
Tunnel vision in criminal cases occurs when investigators commit to a suspect or theory early and filter all subsequent evidence through that commitment.
Structured techniques such as "consider the opposite," competing-hypothesis analysis and devil's advocate roles can reduce the risk.
The goal is not to avoid hypotheses but to hold them lightly, treating them as guides for inquiry rather than conclusions to defend.
Research shows that even awareness of confirmation bias is not enough on its own; investigators need practical procedures that force alternative thinking.

Why do investigators get attached to a theory?

The tendency to favour confirming evidence is deeply rooted in human cognition. Nickerson's 1998 review of confirmation bias in the Review of General Psychology surveyed more than two hundred studies and concluded it was "one of the most extensively studied and well-established" biases in the field. People do not simply prefer supporting evidence; they actively interpret ambiguous information as consistent with what they already believe.

In investigation, several factors make this worse:

Early commitment. Once an investigator identifies a primary suspect, time, resources and public statements are invested in that direction. Walking it back carries professional and psychological costs.
Need for closure. Ask and Granhag's 2005 study found that investigators with a high need for cognitive closure were less sensitive to exonerating information when it contradicted their initial hypothesis. The pressure to close a case can accelerate premature commitment.
Belief perseverance. Even when the original basis for a belief is discredited, the belief itself tends to persist. This is what psychologists call belief perseverance, and it means that withdrawing a piece of evidence does not automatically undo the conclusion it once supported.
Social reinforcement. Findley and Scott (2006) noted that the longer investigators live with a conclusion, repeating it and building on it, the more entrenched it becomes. Colleagues, supervisors and prosecutors who share the theory reinforce it further.

What does tunnel vision look like in practice?

Investigative tunnel vision is the downstream consequence of unchecked confirmation bias. Findley and Scott described it as a process where investigators "focus on a suspect, select and filter the evidence that will 'build a case' for conviction, while ignoring or suppressing evidence that points away from guilt."

This does not require bad faith. An investigator can genuinely believe they are following the evidence while unconsciously giving more weight to facts that fit their theory and less weight to facts that do not. Ambiguous evidence gets interpreted as incriminating. Witnesses who support the theory are treated as credible; those who do not are treated as mistaken or uncooperative. Physical evidence that could fit multiple explanations is read as fitting only one. For a closer look at how a single piece of evidence can support more than one reading, see can one piece of evidence support more than one theory.

What practical techniques help investigators stay open?

Research and professional practice suggest several structured approaches:

Consider the opposite

One of the most studied debiasing techniques is simply asking "what if I am wrong?" Before committing to a conclusion, the investigator lists the strongest reasons the current theory might be incorrect. Lilienfeld and colleagues' 2009 review in Perspectives on Psychological Science found that this approach has empirical support for reducing confirmation bias. In forensic investigation contexts, Rassin tested a "consider the opposite" intervention and found it effective at reducing biased judgement.

Competing-hypothesis analysis

Rather than testing a single theory, investigators can maintain two or more competing hypotheses and evaluate each piece of evidence against all of them. This is the basis of testing competing hypotheses in structured analytical methods. The key step is to ask, for each new piece of evidence, whether it distinguishes between the hypotheses or whether it is equally consistent with more than one.

Devil's advocate and red teams

Assigning someone the explicit role of challenging the working theory forces the team to confront weaknesses. This can be a colleague, a supervisor reviewing the case, or a formal review board. The value is not that the devil's advocate is necessarily right, but that the exercise surfaces assumptions that might otherwise go unexamined.

Searching for disconfirming evidence

Instead of asking "what evidence supports my theory?", the investigator asks "what evidence would I expect to find if my theory were wrong, and have I looked for it?" This is the practical application of actively open-minded thinking. Wason's 1960 experiment demonstrated that people rarely try to falsify their own hypotheses, but that those who do are far more likely to reach the correct answer.

Documentation and review

Writing down the reasons for pursuing a particular line of inquiry, and the evidence that does and does not support it, creates a record that can be reviewed later. When the theory shifts, earlier reasoning can be checked for bias. Regular case reviews by someone not emotionally invested in the current theory also help.

Is awareness of bias enough?

Not on its own. Research consistently shows that knowing about confirmation bias does not reliably prevent it. Ask and Granhag's 2005 study used experienced criminal investigators, not untrained students, and still found confirmation effects. Nickerson (1998) noted that people who are aware of the bias can still fall into it because the processing happens automatically. What helps is not awareness alone but structured procedures that require alternative thinking as a routine part of the investigation, not an afterthought.

How does Murder Book put this into practice?

Murder Book: The Art of Interrogation is an upcoming narrative interrogation game from Gungrounds, an independent studio in Zagreb, Croatia. Development screenshots show an evidence board where players link statements such as "I NEVER met her!" and "I had no idea" to other evidence, and a branching case map with achievement endings and a completion percentage. The case select screen includes a "not guilty" result, which means players can, and sometimes should, conclude that a suspect is not responsible.

This design mirrors the investigative challenge described above. The game gives players behaviours to observe, including Fabrication, Avoidance and Narrative Gaps, but leaves open the possibility that those behaviours have innocent explanations. Committing too early to one reading of the suspect's story means missing branches, overlooking contradictions, or reaching the wrong conclusion entirely. The structure rewards players who consider alternative explanations rather than locking in on the first theory that seems to fit.

Murder Book is in development for PC (Steam) and mobile, with release currently planned for the end of Q2 2027.