Forensic Psychology at the University of Nottingham

November 29, 2020, by Kate

The Forensic Ideas Series #1

#1 A lesson from Forensic Science

I am fascinated by the ways in which people can have an impact on others where it is not obvious how that is achieved; the art of persuasion, The Forer Effect, Cold Reading, some of the well-known illusions performed by Derren Brown, the use of ‘nudge’ to change behaviour, even the ethically dubious and possibly made up techniques of the PUA community. In this vein, I wonder is there another principle, from forensic science, that might have value for the forensic psychologist to consider, which could link to intuitive communication and clinical intuition?

Learning from Horatio Caine

For many of us TV programmes like CSI: Miami, with the magnificent David Caruso, are a welcome escape from work. Although they may be cliched police procedurals they have provided something of a window on the workings of forensic science, where a single fibre links someone to a murder, and justice prevails. It has also resulted in the rumour of a CSI Syndrome or CSI effect, whereby our belief in the power of forensic science is alleged to influence the behaviour of juries. There is little psychology, other than Horatio’s well-timed removal of his sunglasses to emphasise time and again that crime does not pay. So why would we think that we could learn anything from Horatio Caine?

I think there are two things we can learn, one of them really very important. The less important is that people who use the term ‘forensics’ as a short form of forensic psychology are actually referring to forensic science so appear to be confused. However, there is an important, subtle perspective we can borrow from forensic science, and one that may be of great value in circumstances where our best efforts, our assessment, formulations, and interventions, don’t seem to work. It won’t act as a solution to these situations but might offer a strategy to elicit change.

Horatio and Locard

Almost every CSI episode, and Horatio’s genius, relies on a principle described by Edmond Locard, a French forensic scientist, who suggested that whenever something comes into contact with something else, both items retain evidence of that contact. In simple terms, if two cars hit each other Locard’s Principle states that both will leave traces of their paint on the other car, or at the scene of the crash. If you can identify the paint that is on car A or at the scene, which doesn’t belong to car A, then you can identify car B.

Kirk (1953) describes it as follows;

Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibres from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him.

From Locard to forensic psychology

Locard’s Principle is about contact, so where does that link to forensic psychology? At a very gross level we could imagine that we make psychological ‘contact’ through assessments and interventions, and that’s probably true, but these are interactions with the intention of producing change, leaving some kind of impact on our clients; this is not accidental. If you are able to provoke, encourage, support, engender change through your interventions you are fulfilling your role.

But what if you can’t? What if a client won’t engage with you or engages but only to tell you that they can’t change, won’t change, that they are only ‘doing psychology’ because they have been told it will impact on their release date? Is it possible that we can still influence them in a positive way, or move them to become more likely to engage with psychology, without directly doing psychology?
I think so, because I think Locard’s Principle applies simply when we are around people. You are seen and that is interpreted, you behave and that is interpreted, all manner of implications are made about you because you are present in the environment. Just by being present there is psychological transference taking place when you are seen or heard. You leave psychological traces on everyone who perceives you. This shouldn’t be such a surprise as research has suggested that there can be a great degree of ‘understanding’ between people without communication (see Bass, 2015; Campbell & Pile, 2015). It also fits rather well with Gibson’s idea of perception, that objects in the environment contain information about how they can be used, what Gibson referred to as affordances. Is it plausible that we each have psychological affordances that can be perceived by others? Isn’t this the basis of the idea that body language allows us to understand other people (yes, if she crosses her legs and her shoe points towards you, she fancies you. It’s science). If you believe that behaviour has meaning it seems to follow that you accept some sense of psychological affordances.

Normally we don’t worry about this and actually don’t have the capacity to, as it implies that you are impacting everyone in the supermarket, everyone on the train, and we can’t expect to manage so many interactions. But these impacts are likely to be slight, certainly over the short-term. We also can’t specify what works as we don’t know what is being transferred nor do we know how it will be integrated and interpreted. Wait, so you’ve just spent time reading about something that might be important only to discover you have no control over what you transmit, if anything, or how it could be interpreted, if it is… So why worry about it?

I think there are two answers to this question.

If we aren’t in control of Locard’s Principle, why worry?

1) Simply because it is happening and to deny that it is happening leaves us ignorant of a factor that will influence everything that we do with our clients and has the possibility of impacting our clients just by us being in their environment, whether specifically with them or just in their more general environment. If we naïvely believe that it is only when we plan to produce change that change happens, we are misunderstanding the complexity of human interaction and will only search for explanations in what we know that we consciously do.

2) I think we reach a point, over time and with experience, when we may not know what is working, but we know that something is working, and that intuition can be an important guide to help us manage our interactions with others. There is a growing body of evidence that clinical intuition plays an important role in working with clients (Jeffrey & Fish, 2011). My suggestion is that we do have an impact upon people, and with experience we can hypothesise what it is that is having that impact, and potentially use that in our work. A series of small changes can lead to big changes, and sometimes only small changes are required to make a big difference.

Is this just ‘modelling’?

Some people might say that this idea is just modelling by another name, but I think there is an important difference. When we use modelling, we are demonstrating specific behaviours that we hope our client will start to imitate, and even though this is carried out without verbal description the aim is to produce a defined change. For me modelling is another therapeutic tool that we purposefully engage in, whereas Locard’s Principle is not intentional at the start.

Are there downsides if Locard’s Principle is at work in forensic psychology?

Yes, for two reasons.

1) We don’t know what impressions, what traces, we may be leaving behind, or how they may become integrated into that other person’s experience and understanding. I believe that we do discover a sense of what the consequences of these transferences are as we gain more experience of clients, of work, of noticing the nuances of working as psychologists, so we can work to reduce the negative impact we might have and build on the positive.

2) It works both ways, so just as you and your behaviour can impact upon your client, they and their behaviour can impact upon you, and we don’t necessarily know how because it isn’t a conscious, intentional process – we don’t decide on what “bears mute witness against us”. That’s why supervision is so important as that process can make us aware of the unconscious influences on us, even if we cannot identify what they actually are.

I have no evidence to support this idea and am not sure I could design a study to test it. However, I find it useful for reflecting on my work with clients, to think beyond the overt communication, and consider how being present, both physically and psychologically, can be used to make a difference. It also reminds me that a lot of the time complex psychological theories are for psychologists (as Usher (1986) wrote, “Are such theories telling us something empirically necessary about the world or something subject to cultural contingency and local variation?”) and people have been learning, developing, and changing far longer than psychology has been around.


Side note

One reason why I think our current remote teaching, supervision, and meetings are so treacherously dull and empty is because much of this important unconscious transference is not taking place; it’s harder to understand people, to predict the flow of a conversation, to pick up on the important subtleties of one another when we are not physically present. Someone should do a research project on the death of humanity by Teams.


Bass, A. (2015). The dialogue of unconsciousness, mutual analysis and the use of self in contemporary relational psychoanalysis. Psychoanalytic Dialogues, 25, 2-17.
Campbell, J. & Pile, S. (2015). Passionate forms and the problem of subjectivity: Freud, Frau Emmy von N. and the unconscious communication of affect. Subjectivity, 8, 1-24.
Gibson, J.J. & Crooks, L.E. (1938). A Theoretical Field-Analysis of Automobile-Driving. The American Journal of Psychology, 51(3), 453-471. Gibson’s best known work appears in his various books, but this early paper gives a flavour of his idea.
Jeffrey, A. J. & Fish, L. S. (2011). Clinical intuition: A qualitative study of its use and experience among marriage and family therapists. Contemporary Family Therapy, 33, 348-363.
Kirk, P.L. (1953). Crime investigation: Physical evidence and the police laboratory. New York: Interscience Publishers, Inc.


The Forer Effect

Cold Reading

Derren Brown


David Caruso


The CSI effect

Usher, R.S. (1986)


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