How to think like a detective

Need to know

A criminal investigation is a complex, multifaceted problem-solving challenge. Detectives must make critical decisions rapidly – sometimes involving life and death, based on limited information in a dynamic environment of active and still-evolving events. Detectives are responsible and empowered under the law to make judgment calls that will dramatically affect the lives of those involved. The stakes are high, the settings are ugly, and there’s no room for error.

Detectives are often portrayed as misanthropic masterminds. They seem to possess almost mythical personal gifts that the average person can only dream of. I’m sorry to disappoint you, but this isn’t entirely true. Not all detectives are masterminds, and you actually don’t need to be a detective to think like one. A few tools and methods can improve your inner detective, help you find facts, and learn to better understand the relationship between them.

Most of us, whether we’re highly educated or not, have never actually learnt how to think and make safe judgments under pressure. Yet good thinking is important for every aspect of life. Learning how to think like an expert detective can boost your incisiveness and creativity. It can make you less judgmental and a better listener. Honing your detective-thinking skills could help you solve everyday issues, such as planning the perfect vacation or choosing the best job candidate.

I am a university academic, but I’m also a real-life detective myself – more specifically, I’m a detective chief superintendent at the Norwegian Police University College. I’ve worked on some of the worst crimes in Norway for 30 years. These days, I spend much of my time teaching police detectives and other investigators how to make safer decisions in serious and complex matters – and I’m going to share some of the basics with you in this Guide.

When I first started as a police officer, none of my fellow detectives, police academy teachers or criminal investigation department bosses were seemingly able, nor interested, in telling me in practical terms how to think like a detective. Instead, they talked about attitude, talent and experience. Most of all, they liked talking about old cases they’d solved. They never spoke about the cases they failed to solve or the next challenge. The most crucial tool of any successful investigator – namely, sharp reasoning skills – was also never mentioned. We were all very keen on formulating mental profiles of offenders. Yet, strangely, the idea of profiling the effective detective was almost taboo. It’s as if the ability to think like an expert detective was taken for granted.

In fact, what might at first seem akin to a supernatural gift is mostly a metacognitive skill, which means the ability to think about thinking. Anyone can learn to improve their metacognitive skill, but it doesn’t come easily. For most of us, it goes against our instincts. Consider the common cognitive bias known as WYSIATI or ‘what you see is all there is’, described by the Nobel Prize-winning psychologist Daniel Kahneman in his book Thinking, Fast and Slow (2011). WYSIATI refers to the fact that we typically make our judgments according to the information we have readily available – no matter how incomplete it is. We find it difficult to appreciate that there are still many things we don’t know. Another bias known as ‘confirmation bias’ compounds WYSIATI, and describes our tendency to seek out more evidence to support our existing beliefs or judgments.

Imagine what happens when you meet someone new. It typically takes less than a second to establish an impression of a complete stranger. Immediately, we decide whether they’re empathic and courteous or dominant and hostile, and whether we like them or not. What’s more, we do all this based on gut feeling and incomplete information such as facial features, how the person’s dressed, or how they talk. When we make everyday decisions, our mind often considers only the first information at hand. Regardless of its quality and quantity, the only thing it tries to do with the information is to build a coherent story. ‘He is nice!’, ‘She is not!’ That’s it. The story doesn’t have to be accurate, complete or reliable; it only has to be coherent for us to feel confident in our judgment.

Making decisions this way is easy, comfortable and intuitive, but unfortunately it also fuels feelings of overconfidence and exaggerated competence. Regardless of our social class or our so-called intelligence, we are all by nature ‘cognitive misers’ – that is, we have a tendency to solve problems in superficial and effortless ways rather than via more sophisticated and effortful ways. If not addressed deliberately, this overconfidence, and the gap between one’s initial ideas and reality (see figure above), can lead even the most trusted experts astray.

As a homicide detective, I began to notice how my more skilled colleagues were different from the others. It wasn’t apparent at first. They never spoke loudly nor did they frown at how obvious things were. They didn’t voice their opinion any more than others; they didn’t jump to conclusions. Rather, they observed, asked questions, and calmly kept on digging. This detached involvement and the ability to keep digging are the main attributes that set expert detectives apart from the rest of the crowd. Hence, not making a decision is the best decision a good investigator can make. For some of us, it will be hard, and it might take some practice. It seems counterintuitive to walk away from a problem you want to solve. Forcing your mind to take a step back is not easy.

However, when you get the hang of this way of thinking, you’ll find it helpful in many everyday situations and problems, big or small. For instance, it might help you become less judgmental in social settings, have the patience to acquire more information, and end up a better reader of people. Thinking like a detective will encourage you to continuously analyse any problem until the time is right to start fixing it. When done correctly, over time, your patient approach will also build your trustworthiness and integrity.

In fact, I would go so far as to say that when making any important life decisions where it would be hazardous to jump to conclusions – eg, when buying a new home, hiring a new employee or planning a career move – it’s wise to adopt the same detachment and patient approach as used by expert detectives. Keep in mind that your brain will invariably try to convince you that your first impression is right. So, to activate your inner detective, you will have to make a conscious effort to dig deeper into all the available information, and try to do a more systematic and thorough analysis of the strengths and weaknesses of various conclusions before making your decision. In the next section, I’ll show you the practical steps involved in applying a detective’s mindset to any investigation in your life.

What to do

Step 1: Assume nothing and find out what you really know

To think like an expert detective, you have to embrace a so-called ‘investigative mindset’. The terms ‘possibly’ and ‘could’ should be your watchwords as they are in every real investigation and at every crime scene. In detective handbooks, this is called the ABC principle:

• Assume nothing
• Believe nothing
• Challenge and check everything

Nothing should be taken for granted or accepted at face value. Expert detectives will always take a sceptical approach to any information or evidence. All stories are possible, until they are not. Always ask yourself ‘What do I know?’ and ‘What do I not know?’ Doing this is sometimes very hard, but even just attempting to slow down your otherwise conclusion-jumping brain will prove helpful. Keep reminding yourself: correlation does not imply causation. Hence, the safest way to test any hypothesis is to try to disprove it. Suppose you think your house keys are lost or stolen. In this situation, it might be a good idea to double-check and eliminate all other options before you decide to change your locks. The only true investigative mantra was formulated in 1890 by Arthur Conan Doyle’s fictional detective Sherlock Holmes. It goes like this: ‘[W]hen you have eliminated the impossible, whatever remains, however improbable, must be the truth.’

It might sound pretty straightforward, but believe me, it’s not. There’s a reason why Sherlock Holmes is considered a genius. The hardest thing is to resist our automatic assumptions and deep-seated need for closure.

Step 2: Identify all the possible explanations

In the Sherlock Holmes novels, our titular hero continuously assails Dr Watson, a man of science, about the merits of deductive logic. In fact, strictly speaking, Holmes’s favoured logical approach is not deduction, which is reasoning on the basis of known facts, but rather what is known as abductive logic, which is the cognitive process of identifying the best possible explanation for a given set of observations. Abductive reasoning is widely recognised as a powerful mechanism for hypothetical reasoning in the absence of complete knowledge. It’s generally understood as reasoning from effects to causes. Only rarely does Holmes engage in the deduction of which he speaks so highly.

A familiar and typical application of abductive reasoning is when a doctor makes a medical diagnosis: given a set of symptoms, what is the diagnosis that would best explain most of them? As a general rule – and due to our conclusion-loving brain – there will always be more alternative explanations than you first realised. A wise doctor won’t leap to make the first diagnosis that springs to mind, but will consider many alternatives to see which best matches the presentation before them.

Similarly, criminal investigations are abductive and not deductive. In most cases, the police don’t find a crystal-clear and indisputable CCTV picture of the suspect while he commits a crime. We’ll typically have a greyish, blurred image of a person leaving or entering a dark alley just before, or just after, a crime was committed. Our initial interpretation of the picture might tell us that this potential offender is a relatively tall man in his 40s wearing a short dark jacket and black or blue jeans. The description can, in essence, fit half the city’s population. Hence, to identify a suspect, you have to come up with all the possible interpretations, then cross-check your blurred picture with a number of other sources of information such as witness statements, motives, fingerprints or mobile-phone activity, to find a suspect and rule out other potential candidates.

Similarly, you should always create a short outline of all the possible alternative explanations you can think of for the situation you’re trying to solve. Based on your alternatives, your next important step is to make a plan for the information you need to test your different explanations, including how you’ll get hold of the required information. This will be your investigation plan.

Step 3: Test the alternative explanations and narrow your investigation

Now’s the time to start the real investigation. This is when the Sherlock Holmes mantra about eliminating the impossible kicks in. Try to eliminate as many explanations or lines of inquiry as you can. Just like in science, theories can be truly tested only through falsification. To be able to keep track of all your alternative explanations and information needs, you’ll need to take a methodical approach. Without it, there’s a huge risk you’ll become a slave to your first and best idea. My colleagues and I designed a model to help. It’s in no way perfect, but probably far better than no model at all. We’ve called this the 6-Cs approach:

First of all – what do you know? Collect the available information and check the facts. Are they relevant, accurate and reliable? Connect the dots. Do different sources say the same? Find out what you don’t know. Next, construct all possible solutions and hypotheses. What does the available information allow for? What do we need to check, and what can be cross-checked? What can be ruled out? What remains possible? Now, consider what information you need the most in order to test your remaining hypotheses? Before you implement your plan, always consult somebody you trust, to help narrow the scope of your investigation by repeating this process from step one.

Let’s apply this to a fictional example based in the world of the animated movie Zootopia (aka Zootropolis) (2016): officer Judy is called to Zootopia Town Hall after mayor Lionheart was found lifeless on the floor in the canteen with a deep wound to his head. Beside him is a large candleholder covered in blood marked with fingerprints. Officer Judy takes photos and secures the candleholder, and soon after she finds that the blood is Lionheart’s and that the fingerprints belong to the assistant mayor Dawn Bellwether. Bellwether is called for an interview, but denies any knowledge of, or involvement in, the incident.

Now, imagine you’re assisting officer Judy on this case: what’s your first idea or suspicion? Write that down. Like me, you probably suspect Bellwether of a deliberate attack or even attempted murder of mayor Lionheart by hitting him over the head with a heavy candleholder. To think like a detective, what’s critical at this point is not to jump to conclusions but to start digging.

This is the first step – assume nothing. We need more information. To paraphrase Holmes: data, data, data: you can’t make bricks without clay. Ask yourself, what do we not know? What other sources of information are available? What alternative explanations might fit the evidence?

First, assuming that the fingerprints are related to the episode, Bellwether might accidentally have hit the mayor. Second, perhaps Lionheart was the one who attacked Bellwether, and she hit him in a lawful act of self-defence. These alternatives should definitely be investigated. Third, perhaps Bellwether found the mayor on the floor after somebody else had attacked him and she touched and moved the bloody candleholder. This hypothesis should also be added to your investigation plan. Fourth, although it might seem unlikely, maybe Bellwether and Lionheart were involved in an earlier incident where the mayor cut himself, such as during cooking or decorating, and Bellwether subsequently moved the candleholder with his blood on it. Furthermore, we can’t yet exclude that someone is trying to frame Bellwether by staging the event. Is that possible? Does she have enemies? If the answer is yes, you have yet another hypothesis that should be addressed. Now, since our investigation rests solely on the conclusion of a fingerprint expert, we should also double-check if another independent expert will come to the same conclusion. Sadly, in real life, there are plenty of examples of botched forensic evidence leading to wrongful convictions. Finally, we must check whether Bellwether hit mayor Lionheart but was somehow not in complete control of her faculties while she did so, hence her lack of memory for the incident.

Use a mind map

As you can see, there are more alternative options than you perhaps thought of in the beginning. To assist our fragile minds, we need practical methods and information-handling tools to keep track of our investigations. This will help your brain be more accurate, and reduces the risk of it jumping to premature conclusions. So you should keep track of your investigation using a matrix or a ‘mind map’ that lists the upcoming sources of further information against all the alternative explanations for the crime scene (see table below). This will also create transparency, allowing for a second opinion on your ideas and judgments, and you’ll gradually see if information from different sources narrows your investigation.

As each new nugget of information is obtained, you mark on the matrix what it means for each of the different possible explanations or hypotheses. The judgment symbols in the matrix have three different codes: the green plus-sign means that the explanation is supported; a red minus-sign means that an incoming fact opposes the hypothesis, whereas N/A means that the information doesn’t inform or have any bearing upon the hypothesis. The hypotheses that attract the most opposition or minus symbols can gradually be dismissed, while you move forward with the ones that receive more support. Your investigation should document all relevant hypotheses identified in the case, and the inquiry should seek to disprove each one. The last remaining hypothesis is probably the strongest theory but, as a true detective, you should ideally leave it up to others to make the final judgment.

All this nitty-gritty crosschecking is what ‘digging deep’ looks like. You can measure your investigation’s quality on both axes of the matrix: a glance at your number and range of hypotheses will tell you if you have gone wide enough to capture the true potential solution, and your investigative actions will tell you whether you’ve dug deep enough to find the facts to prove or disprove the different hypotheses. In other words, you need to consider both the breadth and the depth of your inquiry.

Recruit a ‘devil’s advocate’

As a rule, in any investigation there will always be something you’ve forgotten or don’t know everything about. That is why an open-minded and critical friend, like Dr Watson in the Sherlock Holmes stories, is so indispensable. As Holmes said: ‘You have a grand gift of silence, Watson. It makes you quite invaluable as a companion.’ He is the so-called ‘devil’s advocate’. Dr Watson’s role is not to solve the case, but to be sceptical and point to things that Holmes might have overlooked or misunderstood.

Remember that evidence, new perspectives or insights can be found where you least expect them. That’s why all expert detectives should demonstrate empathy, be humble, ask questions, and develop their listening skills. Investigative interviewing is done by gently holding back your own opinion, asking open-ended questions, and using silence and active listening techniques such as nodding and humming. This extends to listening to your devil’s advocate. Receptivity to alternative views is a crucial skill not only for detectives, but for any decision-maker in the modern era. In a world where complexity increases constantly, there’s no room for lone wolves.

Links & books

To develop your thinking skills, you need regular training and feedback. Can you solve the three switches puzzle hosted by Guardian News on YouTube? Clue: it helps to start thinking like a detective.

When it comes to examining your existing beliefs, perspective is everything. Are you prone to defending your viewpoint at all costs, like a soldier, or are you spurred on by curiosity, like a scout? In her TED talk ‘Why You Think You’re Right – Even If You’re Wrong’ (2016), the rationalist Julia Galef examines the motivations behind these two different mindsets and how they shape our interpretations of information. When your steadfast opinions are tested, Galef asks: ‘What do you most yearn for? Do you yearn to defend your own beliefs, or do you yearn to see the world as clearly as you possibly can?’

In this blog post for the UK’s Foreign, Commonwealth and Development Office, Gisle Kvanvig and I told the story of how, building on the work of British experts, we used the idea of a detective mindset to inform a new, more ethical approach to interviewing and investigation techniques in, for example, law enforcement. Following this approach, officers are trained to handle the interview room much like a crime scene where accurate, reliable and actionable information can be collected for the purpose of investigating the case.

The book Blackstone’s Senior Investigating Officers’ Handbook (5th ed, 2019) by Tony Cook is a unique one-stop guide to all the processes and actions involved in conducting major investigations, presented in a clear and understandable fashion.

For my PhD thesis The Making of an Expert Detective: Thinking and Deciding in Criminal Investigations (2016), I drew on theoretical frameworks developed in social and cognitive psychology to examine the degree to which individual and systemic factors can compensate for inherent biases in criminal detectives’ judgments and decision-making.

The book The Routledge International Handbook of Legal and Investigative Psychology (2019), edited by the psychologists Ray Bull and Iris Blandón-Gitlin, explores contemporary topics in psychological science, applying them to investigative and legal procedures. Featuring contributions from recognised scholars from around the globe (including myself), it brings together current research, emerging trends, and cutting-edge debates in a single comprehensive and authoritative volume.

The book Superforecasting: The Art and Science of Prediction (2015) by the political scientist Philip E Tetlock and the author Dan Gardner offers a deeper insight into prediction, drawing on decades of research and the results of a massive, US government-funded forecasting tournament. The Good Judgment Project involves tens of thousands of ordinary people – including a Brooklyn filmmaker, a retired pipe-installer, and a former ballroom dancer – who set out to forecast global events. Some of the volunteers have turned out to be astonishingly good. These ‘superforecasters’ have beaten other benchmarks, competitors and prediction markets. They’ve even beaten the collective judgment of intelligence analysts with access to classified information.

‘Correlation does not imply causation’: for decades, this mantra was invoked by scientists in order to avoid taking positions as to whether one thing caused another, such as smoking and cancer, or carbon dioxide and climate change. But today, that taboo is dead. The causal revolution has (seemingly) cut through a century of confusion, and placed cause and effect on a firm scientific basis. The Book of Why (2018) by the computer scientist Judea Pearl and the science writer Dana Mackenzie explains causal thinking to general readers, showing how it allows us to explore both the world that is and the worlds that could have been. It is the essence of human and artificial intelligence. And just as these scientific discoveries have enabled machines to think better, The Book of Why explains how we too can think better.