Case File 285 · Investigation Psychology
What Is a Theory of the Case?
A theory of the case is the overall narrative an investigator, prosecutor or defence attorney constructs to explain what happened, who was involved, and why. It ties together physical evidence, witnes
A theory of the case is the overall narrative an investigator, prosecutor or defence attorney constructs to explain what happened, who was involved, and why. It ties together physical evidence, witness accounts and circumstantial details into a coherent story that accounts for the known facts. In criminal investigation, a theory of the case guides which leads to pursue, which evidence to prioritise, and how to interpret ambiguous information. The concept appears in both investigative and legal contexts, but its function is the same: to provide a working framework that can be tested, refined or abandoned as new evidence emerges.
Key takeaways
- A theory of the case is a structured narrative that explains who committed a crime, how and why, based on available evidence.
- It serves as a working framework that should be tested against new evidence rather than treated as a fixed conclusion.
- A good theory accounts for all known evidence, including facts that do not neatly fit the preferred explanation.
- The danger arises when investigators become committed to a single theory and stop considering alternatives, a problem researchers call tunnel vision.
- Competing theories should be maintained and evaluated side by side until evidence clearly favours one explanation over others.
How is a theory of the case used in an investigation?
In the investigative phase, a theory of the case is a working hypothesis. Detectives review the available evidence, including the crime scene, witness statements and forensic results, and construct a preliminary account of what may have happened. This theory then directs the investigation: it suggests which witnesses to re-interview, which records to obtain, and which physical evidence to test.
The theory is not supposed to be a conclusion reached early and then defended. Rossmo (2009), in Criminal Investigative Failures, argues that investigators must treat their theory as something to be tested rather than confirmed. When new evidence contradicts the working theory, the theory should change. When it does not, the result is often investigative tunnel vision.
How does a theory of the case work in court?
In a trial setting, a theory of the case takes on a more formal role. Both prosecution and defence present their theories to the judge or jury. The prosecution's theory typically lays out the sequence of events, the suspect's motive and opportunity, and how the evidence demonstrates guilt beyond reasonable doubt. The defence may present an alternative theory that explains the same evidence in a way consistent with innocence, or it may challenge the prosecution's theory by highlighting gaps and contradictions.
The International Bar Association's Defence Wiki describes a theory of the case as "a detailed, coherent, accurate story of what occurred" that combines legal elements (the charges and applicable law) with factual elements (the events as the evidence shows them). A strong theory accounts for unfavourable evidence rather than ignoring it, because a jury that notices unexplained facts may lose confidence in the entire narrative.
What makes a theory strong or weak?
A strong theory of the case has several qualities:
- Completeness. It accounts for all the significant evidence, not just the pieces that support the preferred conclusion. Evidence that seems to point away from the theory needs to be addressed, not ignored.
- Internal consistency. The narrative does not contradict itself. Timelines, witness accounts and physical evidence fit together without requiring the listener to accept incompatible facts.
- Testability. The theory makes predictions that can be checked. If the theory says the suspect entered through a back window, there should be physical evidence at that window. If there is none, the theory needs revision.
- Simplicity. While criminal cases can be complex, a theory that requires too many unlikely coincidences or unsupported assumptions is weaker than one that explains the facts more directly.
A weak theory, by contrast, relies on assumptions that cannot be tested, ignores inconvenient evidence, or requires the listener to accept that multiple unrelated coincidences all happened to point toward the same suspect.
Why is it dangerous to commit to one theory too early?
Findley and Scott (2006) published "The Multiple Dimensions of Tunnel Vision in Criminal Cases" in the Wisconsin Law Review, arguing that tunnel vision is a central factor in wrongful convictions. They described how investigators, prosecutors and even defence lawyers can become so focused on a particular conclusion that they "select and filter the evidence that will build a case for conviction, while ignoring or suppressing evidence that points away from guilt."
The problem is not that investigators form theories. They have to. The problem is that once a theory feels settled, cognitive biases make it difficult to abandon. Confirmation bias leads people to seek and interpret evidence in ways that support their existing belief. Belief perseverance means that even when the evidence behind a belief is discredited, the belief itself can persist.
Rossmo (2009) notes that investigators should maintain multiple theories and evaluate them against one another, rather than settling on a single explanation and looking only for evidence that confirms it. For a closer look at how this works in practice, see How Do Investigators Test Competing Hypotheses?.
How should a theory of the case evolve?
A well-managed investigation treats the theory of the case as a living document. Early in an investigation, the theory may be broad and tentative: several suspects, several possible motives, several sequences of events. As evidence accumulates, some possibilities are ruled out and the theory narrows.
The critical discipline is to let the evidence drive the narrowing, not the other way around. When investigators start selecting evidence to fit a theory they have already settled on, the investigation is working backwards. The question shifts from "What does the evidence show?" to "How can I make the evidence support my conclusion?" This is the pattern Findley and Scott identified in case after case of wrongful conviction.
Practical steps include:
- Writing down the current theory and listing what evidence supports it, what evidence contradicts it, and what evidence is missing.
- Maintaining at least one alternative explanation and asking what evidence would be needed to support it.
- Periodically reviewing the case with someone who was not involved in forming the original theory, to get a fresh perspective.
- Asking whether the evidence could support more than one theory.
How does this connect to Murder Book?
Murder Book: The Art of Interrogation is an upcoming narrative interrogation game from Gungrounds in which players construct their own theory of each case. Development screenshots show a branching case map with achievement endings and a completion percentage, suggesting that different interpretations of the evidence lead to different outcomes, including a "not guilty" result.
The game's structure mirrors the investigative principle that a theory of the case must be built from evidence, not assumed from the start. Players examine unreliable stories, behavioural changes and contradictions, and must decide which narrative best accounts for what they have found. Getting it wrong is a real possibility, which is what makes the exercise meaningful.
Murder Book is in development for PC (Steam) and mobile, with release currently planned for the end of Q2 2027.