The Murder Book Casebook
Investigation Psychology
- What Is a Murder Book? The Police Case File ExplainedWhat investigators mean by a murder book, what a homicide case file usually contains, and where the term shows up in crime fiction and games.
- Can You Actually Tell When Someone Is Lying?What decades of research say about how accurately people can tell lies from truths, and why behaviour alone is a weak guide.
- Why There Is No Single Reliable Sign of DeceptionWhy research has found no behaviour that reliably reveals a lie, and why nervous or evasive behaviour has many innocent explanations.
- How Investigators Find Inconsistencies in a StoryA high-level look at how investigators gather an account, test it against what is known and treat inconsistencies with care.
- What Is Cognitive Load in an Interrogation?What cognitive load means in interview research, what the cognitive approach to lie detection proposes, and where the evidence is disputed.
- Interview Versus Interrogation: What Is the Difference?How information-gathering interviews differ from accusatorial interrogations, from the PEACE model to the Reid technique and the research on confessions.
- Open-Ended Versus Leading QuestionsHow open-ended and leading questions differ, what memory research shows about suggestive wording, and why interview guidance puts open questions first.
- Why Truthful Accounts Can Still Be InconsistentWhy a truthful account can shift between tellings, what research says about details remembered later, and when inconsistency does and does not matter.
- Why Innocent People Sometimes ConfessWhat research by Saul Kassin and others shows about why innocent people confess, who is most at risk, and why false confessions are so persuasive.
- How Confirmation Bias Can Affect an InvestigationHow early beliefs can narrow an investigation into tunnel vision, what experiments show about its effects, and which safeguards are proposed.
- What Is an Investigative Timeline?What an investigative timeline is, what it records, how it helps compare accounts, and why its entries must be treated with care.
- How Investigators Compare Multiple AccountsHow investigators compare statements from different people, and why neither agreement nor disagreement settles what really happened.
- Why Memory Is Not a Perfect RecordingWhy human memory rebuilds events rather than replaying them, and what that means for honest witnesses and investigations.
- What Makes a Statement Unreliable?The many reasons a statement can be wrong, from stress and suggestion to source confusion and interview pressure, and why unreliable does not mean dishonest.
- What Is Behavioral Leakage?The origin of the idea that hidden feelings leak through nonverbal behaviour, what the research found, and why leakage is not proof of deception.
- Why People Avoid Answering Questions DirectlyThe innocent and non-innocent reasons people sidestep questions, and why avoidance alone cannot reveal guilt.
- How Repeated Questioning Can Affect MemoryRepeated questioning can bring back genuine details or plant false ones, depending on what the interviewer adds and repeats each time.
- How Stress Affects TestimonyHigh stress tends to make eyewitness memory less accurate, and visible stress in an interview is not a reliable sign of deception.
- What Is the Difference Between a Lie and a False Memory?A lie and a false memory can produce the same wrong statement, but only the liar knows it is untrue.
- How Investigators Test an AlibiInvestigators test an alibi by seeking independent corroboration, but research shows innocent people often struggle to give accurate, well-supported alibis.
- Is Avoiding Eye Contact a Sign of Lying?No. Avoiding eye contact is not a reliable sign of lying. It is the most common belief about liars in the world, but the research does not support it. When people lie, the amount they look away does n
- Is Over-Explaining a Sign of Lying?No. Over-explaining is not a reliable sign of lying. The idea that a long, detailed, unprompted answer betrays a guilty conscience is popular, but it does not hold up. If anything, controlled research
- Are Microexpressions Reliable for Detecting Lies?No, microexpressions are not a reliable way to detect lies. A microexpression is a very brief facial expression, lasting roughly 1/25 to 1/5 of a second, thought to flash when someone tries to conceal
- Is Nervousness a Sign That Someone Is Lying?No. Nervousness is not a reliable sign that someone is lying. It is one of the oldest assumptions in the world about deceit, and it is one of the least dependable. The core problem is simple: anxiety
- Does Looking Left or Right Mean Someone Is Lying?No. The idea that a person looking up and to one side is lying, while looking to the other side means they are telling the truth, comes from neuro-linguistic programming (NLP), not from established sc
- Do Liars Pause Longer Before Answering?Not reliably. Some laboratory research has found that people take slightly longer to respond when lying than when telling the truth, but the effect is small, inconsistent and depends heavily on circum
- Do Liars Give Too Much or Too Little Detail?On average, liars tend to give *fewer* details than truth tellers, but the amount of detail alone is a weak and unreliable guide to honesty. People vary enormously in how much they say, and an honest
- Is Defensiveness a Sign of Lying?No. Defensiveness is an emotional reaction to feeling accused or disbelieved, not a reliable indicator of lying. Innocent people frequently become defensive, irritated or protective of themselves prec
- What Does It Mean When Someone Changes Their Story?A changed story is not proof that someone is lying. People revise what they say for many ordinary reasons. Memory is reconstructive and shifts a little each time it is recalled; a later telling can su
- Why Do People Say I Don't Remember During Questioning?"I don't remember" is usually a true statement about the state of someone's memory, not a confession or a dodge. Forgetting is the normal fate of most of what we experience; detail fades quickly, and
- Can Body Language Tell You If Someone Is Lying?No. Body language cannot tell you reliably whether someone is lying. The popular signs — avoiding eye contact, fidgeting, crossed arms, touching the face — are not dependable indicators of deception.
- Why Do People Avoid Answering a Question?People avoid answering questions for many reasons, most of which have nothing to do with guilt. A question can be intrusive, unfair, confusing or unanswerable; the person may not know, may need to pro
- What Is Deflection in a Conversation?Deflection is a way of steering a conversation away from a topic or away from yourself instead of engaging with what was actually asked. In practice it can mean changing the subject, answering a quest
- Deflection vs Avoidance: What Is the Difference?Deflection and avoidance are both ways of not dealing with a question head-on, but they work differently. Avoidance means staying off a topic — declining to go there, giving a non-answer, or falling s
- What Is Omission, and Is Leaving Something Out the Same as Lying?Omission means leaving something out — withholding information rather than stating something false. Whether that counts as "lying" depends on who you ask. Many philosophers hold that a lie requires an
- Omission vs Fabrication: What Is the Difference?Omission and fabrication are two different ways of misleading. Omission means leaving true information out — concealing. Fabrication means putting false information in — asserting something untrue. Bo
- What Is a Scripted Response?A scripted response is an answer that follows a set pattern instead of being put together fresh on the spot. In everyday speech, calling a reply "scripted" means it sounds rehearsed, formulaic or reci
- Can a Rehearsed Story Still Be True?Yes. Rehearsing an account does not make it false, and a well-practised story is not evidence of deception. Honest people rehearse all the time: they run through what they will say before a job interv
- Why Do People Revise Their Story During Questioning?People revise their story during questioning for many ordinary reasons, and most of them have nothing to do with lying. Human memory is reconstructive, not a recording, so an account is rebuilt each t
- What Is Selective Memory?"Selective memory" is the everyday phrase for remembering some things clearly while forgetting or overlooking others. It is not a medical condition, and it is not proof that someone is being dishonest
- Is Selective Memory Evidence of Lying?No. Selective memory, meaning recalling some parts of an event clearly while forgetting or misremembering others, is a normal feature of how human memory works rather than reliable evidence that a per
- What Is an Emotional Appeal During Questioning?An emotional appeal during questioning is any move by an interviewer that works on how a person feels, through sympathy, guilt, relief, hope, pride or fear, rather than on the facts, in order to encou
- Why Do People Justify Their Actions Instead of Denying Them?When people are challenged, they often justify what they did, arguing it was reasonable or understandable, rather than flatly denying it. They do this for well-studied psychological and social reasons
- Why Do People Shift Blame When Questioned?People shift blame when questioned because moving responsibility onto someone or something else is a fast, self-protective response that eases guilt and defends a person's self-image. Psychology has d
- What Does Cooperation Look Like in an Investigative Interview?Cooperation in an investigative interview means a person engages with the process: they turn up, stay, answer the questions put to them and give an account of what they know. It is a pattern of behavi
- Is Silence a Sign of Guilt?No. Staying silent is not proof of guilt. It is a legal right, and it has many innocent explanations: fear, confusion, distrust of the process, the advice of a lawyer, or simply not knowing the answer
- Why Might an Innocent Person Refuse to Answer Questions?An innocent person may refuse to answer questions for reasons that have nothing to do with having something to hide. They may have been advised by a lawyer to stay quiet. They may fear being trapped o
- Is Inconsistent Behaviour Evidence of Deception?No, inconsistent behaviour is not reliable evidence of deception. When a person's account changes, their manner shifts, or their story does not quite line up from one telling to the next, it is tempti
- What Is the Misinformation Effect?The misinformation effect is a change in how someone remembers an event after they are exposed to misleading information about it afterwards. If a witness sees something, and then reads, hears or is a
- Does Eyewitness Confidence Mean the Memory Is Accurate?Not on its own. How sure a witness feels is not a direct readout of how accurate their memory is, because confidence can be shaped by things that have nothing to do with what they saw. The research is
- Why Can a Confident Witness Still Be Wrong?A confident witness can be wrong because confidence and accuracy are produced by the same memory system, and that system is reconstructive and open to influence. A person can hold a vivid, detailed, s
- What Is Memory Contamination?Memory contamination is what happens when a person's memory of an event is altered by information that reaches them after the event, so that their later account mixes what they actually experienced wi
- Can Witnesses Change Each Other's Memories?When witnesses to the same event talk to each other before giving their accounts, their memories can merge. Details one person saw can transfer into another person's recollection, and the recipient of
- What Is Memory Conformity?Memory conformity is the tendency for people's accounts of a shared event to become more similar after they interact. When witnesses talk about what happened, compare notes or even just overhear each
- Why Can Two Honest Witnesses Remember the Same Event Differently?Two honest witnesses can remember the same event differently because memory is not a recording. Each person encodes only a fraction of what happens, filtered by where they were standing, what they wer
- How Does Time Affect Eyewitness Memory?Time weakens eyewitness memory. The longer the gap between witnessing an event and being asked to recall it, the less complete and less accurate the account tends to be. This is not controversial; it
- Can New Information Change an Old Memory?Yes. Information a person encounters *after* an event, called post-event information, can change what they later remember about it. When someone reads a news report, hears another witness, or is asked
- What Is Source-Monitoring Error?A source-monitoring error happens when you remember a piece of information correctly but misremember *where* it came from. The detail is real; the source is wrong. You might recall a fact but not whet
- How Reliable Is Eyewitness Testimony?Eyewitness testimony is useful but far less reliable than it feels, to the witness or to the people hearing it. Memory is not a recording. It is reconstructed each time it is recalled, and it can be i
- Does Trauma Make Memory More or Less Accurate?Trauma and high stress tend to make eyewitness memory *less* accurate, not more, which runs against the common belief that a frightening event burns itself in perfectly. The research is more nuanced t
- How Does Alcohol Affect Eyewitness Memory?Alcohol impairs eyewitness memory, but the relationship is more nuanced than a simple "drunk witnesses are unreliable." Research shows that the effects depend on how much was consumed, when it was con
- How Does Sleep Deprivation Affect Memory and Questioning?Sleep deprivation weakens memory, impairs judgement and increases susceptibility to suggestion, all of which matter when a person is being questioned. Research shows that people who have not slept are
- 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
- What Is a Double-Blind Police Lineup?A double-blind lineup is one where neither the witness nor the person administering the lineup knows which member is the suspect. The purpose is to prevent the administrator from influencing the witne
- Why Should Witnesses Be Interviewed Separately?Witnesses should be interviewed separately because people who discuss an event together tend to contaminate each other's memories. Research by Gabbert, Memon and Allan (2003) found that 71% of witness
- Can Repeated Recall Improve Memory?Repeated recall can improve memory, but it can also introduce complications. A landmark 1988 study by Scrivner and Safer found that eyewitnesses who recalled a violent event across four successive tri
- What Are the Three Types of False Confession?The three types of false confession are voluntary, coerced-compliant and coerced-internalized. This classification was introduced by Kassin and Wrightsman in 1985 and remains the most widely used fram
- What Is a Coerced-Compliant False Confession?A coerced-compliant false confession occurs when a suspect confesses to a crime they did not commit in order to escape the pressure of an interrogation, even though they privately know they are innoce
- What Is a Coerced-Internalized False Confession?A coerced-internalized false confession is one in which an innocent person, worn down by a stressful interrogation, actually comes to doubt their own memory and may briefly believe they committed a cr
- What Is a Voluntary False Confession?A voluntary false confession is one that an innocent person offers without any pressure from police. There is no exhausting interrogation and no confrontation with false evidence behind it; the person
- What Is Confession Contamination?Confession contamination happens when details about a crime that only the true perpetrator should know are introduced to a suspect during questioning, so that those facts end up woven into the suspect
- Why Can a False Confession Contain Accurate Crime Details?A false confession can contain accurate crime details because those details are often introduced during the interrogation itself. When investigators share non-public facts, whether deliberately or ina
- Does Interrogation Length Affect False Confession Risk?Yes, interrogation length is one of the most well-documented risk factors for false confessions. A landmark study by Drizin and Leo examined 125 proven false confession cases and found that 84% occurr
- Why Are Young Suspects More Vulnerable to False Confessions?Young suspects are more vulnerable to false confessions because of developmental factors that affect how they respond to interrogation pressure. Research on DNA exonerations has found that juveniles a
- Can Interrogation Pressure Change What Someone Believes Happened?Yes, interrogation pressure can change what a suspect believes happened. In what researchers call a coerced-internalised false confession, an innocent person not only confesses but comes to believe th
- Why Are Confessions So Persuasive to Juries?Confessions are among the most powerful forms of evidence in a criminal trial, and research consistently shows they have a stronger effect on jury verdicts than eyewitness identification, character te
- Does Recording an Entire Interrogation Reduce Problems With Confessions?Yes, recording entire interrogations is one of the most widely supported reforms for reducing problems with confessions. When the full process is captured on video, fact-finders can see what happened
- Can Someone Confess to Something They Do Not Remember Doing?Yes, it is possible for someone to confess to something they do not remember doing, and research shows this happens more often than most people expect. These are known as coerced-internalised false co
- Why Do Innocent People Waive Their Right to Remain Silent?Innocent people waive their right to remain silent primarily because they believe their innocence will protect them. Psychologist Saul Kassin has described this as the "phenomenology of innocence": th
- Can Minimization Sound Like a Promise of Leniency?Yes, research shows that minimisation techniques can function as implied promises of leniency, even though they make no explicit offer. Minimisation is a legal interrogation tactic in which an intervi
- How Can Investigators Check Whether a Confession Is Reliable?A confession is not automatically reliable just because someone said it. Investigators check whether a confession is reliable by looking for independent corroboration: details the suspect provided tha
- 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
- How Do Investigators Test Competing Hypotheses?Investigators test competing hypotheses by evaluating multiple possible explanations for the evidence side by side, rather than picking one theory and looking for proof. The most widely cited framewor
- Why Should Investigators Consider Alternative Explanations?Investigators should consider alternative explanations because the human mind is wired to favour the first plausible account it settles on, and that tendency leads to mistakes. Research on wrongful co
- What Is Corroborating Evidence?Corroborating evidence is any additional evidence that strengthens or confirms evidence already in hand. If a witness says a suspect was at a location at 9 pm, and CCTV footage shows the same person t
- Why Is Corroboration Important in an Investigation?Corroboration matters because no single piece of evidence is perfectly reliable. Eyewitnesses misidentify people, confessions can be false, forensic methods have error rates, and documents can be forg
- Direct Evidence vs Circumstantial Evidence: What's the Difference?Direct evidence proves a fact without requiring any inference. Circumstantial evidence requires the fact-finder to draw a logical conclusion. If a witness testifies "I saw him break the window," that
- What Is Inculpatory Evidence?Inculpatory evidence is evidence that tends to show a person's involvement in a criminal act or helps establish guilt. The word comes from the Latin *inculpare*, meaning to blame. Examples include a w
- What Is Exculpatory Evidence?Exculpatory evidence is any evidence that tends to show a defendant is not guilty of the crime they are charged with, or that reduces the severity of their alleged offence. It can take many forms: a w
- Inculpatory vs Exculpatory EvidenceInculpatory evidence points toward a suspect's guilt; exculpatory evidence points away from it. The distinction matters because a thorough investigation collects and weighs both kinds. Prosecutors in
- What Does It Mean to Challenge Evidence?Challenging evidence means formally questioning whether a piece of evidence should be admitted at trial, or disputing its reliability and weight once it is before the court. In criminal cases, the def
- What Is Evidence Admissibility?Evidence admissibility refers to whether a piece of evidence meets the legal requirements to be considered by a judge or jury at trial. Not everything that seems relevant is automatically allowed in c
- What Is Chain of Custody?Chain of custody is the documented record that tracks a piece of evidence from the moment it is collected until it is presented in court. It logs every person who handled the item, when they received
- What Is Reasonable Doubt?Reasonable doubt is the standard of proof that the prosecution must meet to secure a criminal conviction. If the evidence leaves a juror with a reasonable, fact-based uncertainty about whether the def
- What Is the Burden of Proof in a Criminal Case?In a criminal case, the burden of proof falls on the prosecution. The government must prove the defendant's guilt beyond a reasonable doubt; the defendant does not have to prove anything. This princip
- Motive vs Intent: What Is the Difference?Motive is why a person does something. Intent is the conscious decision to do it. In criminal law, this distinction matters because intent is an element of most crimes that the prosecution must prove,
- Means, Motive and Opportunity: What Do They Mean?Means, motive and opportunity are three concepts investigators use to evaluate whether a suspect could have committed a crime. **Means** is the ability to carry it out, whether through physical streng
- Does Motive Prove Someone Committed a Crime?No. Motive alone does not prove that someone committed a crime. In criminal law, motive is the reason a person may have acted, but it is not a formal element of any offence. A prosecutor does not need
- What Does Opportunity Mean in an Investigation?In a criminal investigation, opportunity means that a suspect was in a position to commit the crime. This usually comes down to physical presence: could the person have been at the scene at the time t
- What Makes an Alibi Strong or Weak?An alibi is strong when it is supported by independent, verifiable evidence that reliably places the suspect somewhere other than the crime scene at the relevant time. Physical evidence, such as a tim
- Can One Piece of Evidence Support More Than One Theory?Yes, a single piece of evidence can legitimately support more than one theory. A witness placing a suspect near a crime scene, for instance, is consistent with guilt but also with the suspect simply l
- What Is Investigative Tunnel Vision?Investigative tunnel vision is the tendency of police, prosecutors or other participants in the criminal justice system to focus on a single suspect or theory and to filter all evidence through that l
- Confirmation Bias vs Tunnel Vision: What's the Difference?Confirmation bias and tunnel vision are related but distinct concepts. Confirmation bias is a general cognitive tendency: people seek, notice and interpret information in ways that support what they a
- What Is Anchoring Bias in an Investigation?Anchoring bias is the tendency to rely too heavily on the first piece of information encountered when making subsequent judgments. In a criminal investigation, the anchor is often the earliest signifi
- What Is Hindsight Bias in Criminal Investigation?Hindsight bias is the tendency to look back at an event and believe it was more predictable than it actually was. In criminal investigation, this means that once a case is solved or a suspect identifi
- What Is Belief Perseverance?Belief perseverance is the tendency to maintain a belief even after the evidence that originally supported it has been shown to be false. In a criminal investigation, this means that once an investiga
- Can Knowing a Suspect's Confession Bias Other Evidence?Yes, knowing that a suspect has confessed can bias how other evidence in the case is evaluated. Researchers call this forensic confirmation bias: the tendency for a confession or other expectation of
- Why Is It Hard to Abandon an Investigation Theory?It is hard because of how human cognition works, not because investigators are careless or dishonest. Once a theory forms, several well-documented psychological processes make it resistant to change:
- What Is Actively Open-Minded Thinking in Investigation?Actively open-minded thinking (AOT) is a thinking disposition defined by the willingness to consider evidence that contradicts your current beliefs, to seek out alternative explanations, and to revise
- How Do Investigators Avoid Falling in Love With One Theory?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 in
- Why Should Evidence That Contradicts Your Theory Matter More?Evidence that contradicts your theory should matter more because it has greater diagnostic value. Confirming evidence tells you your theory *could* be right, but disconfirming evidence tells you somet