Locard’s Principle

Dr Edmond Locard. Brilliant man. French Forensic Scientist, born in the 19th Century, who gave his name to a law that remains fundamental to the investigation of crime in the 21st Century.

Locard’s Principle states, very simply, that:

‘Every Contact Leaves a Trace’.

Picture this…

A Burglar in a back garden – leaving footprints in a flowerbed. Breaks a downstairs window and cuts himself – traces of blood left on fragments of glass. Opens the window and climbs in – catching threads of his clothing on jagged edges. Untidy search and property taken – fingerprints invisible on any number of surfaces. Makes his getaway – car registration captured by hidden camera.

OK, so he’s not the brightest of thieves – but I hope his small story will help to explain the genius of Locard…

We get to the scene and do our job well: recover the footmarks and the fingerprints; retrieve the blood and the fibres; track down and view the CCTV footage.

Evidence of him found at the scene.

And, if we catch up with him quickly enough, we might just discover mud from the garden on the bottom of his shoes; microscopic fragments of glass all over his clothes; ill gotten gains in the boot of his car.

Evidence of the scene found on him.

Because every contact leaves a trace.

It’s a principle that explains how most serious crimes – certainly those that can’t rely on eyewitness evidence – get solved: traces left by the suspect at the scene of the crime; traces from that scene carried by the suspect.

Find these things and we’re most of the way to locking up a burglar.

Or a murderer
Or a slave trader
Or a child abuser
Or a rapist
Or a drug dealer

And so it goes on.

Wherever there is contact, an exchange takes place.

But Locard’s Principle has an application that goes far beyond the prevention and detection of crime.

Seems to me that it applies equally to every kind of human interaction – whether between lifelong friends or passing strangers. Every time two people come into contact with one another, an exchange takes place. Spoken or unspoken; for better or for worse.

Take the working life of a police officer:

• We are the knock on the door in the middle of the night
• We are the headlong rush of blues and twos
• We are the reassuring voice and the shouted command
• We are the bearers of unbearable news
• We are the first ones on scene and the last ones to leave
• We are the helping hand and the shoulder to lean on
• We are the ones you may not want – but, one day, might just need
• We are the ones who don’t always get it right – who are human after all

People tend to remember their encounters with us.

We are entrusted with extraordinary powers on behalf of the communities we serve. We are responsible for the way in which we exercise them. We are responsible, in significant measure at least, for the trace we leave behind.

But not just police officers – the rest of us too…

We smile or we scowl; we encourage or we ignore; we appreciate or we dismiss; we hold out a hand or we withdraw it; we are angry or we forgive; we bless or we curse; we turn away or we walk towards; we give life or we take it; we love or we hate.

And every contact leaves a trace.


2 thoughts on “Locard’s Principle

Add yours

  1. We have a Police Force recognised Globally as a blueprint for excellence & the majority of good people are sensitive to this. We have the best but it needs sustaining & developing to ensure its growth to cope with the future. Every contact leaves a trace! let us hope future contact between Establishment & Policing leaves the right ‘contact’, one the British People can be proud of.

    Liked by 1 person

  2. I’ve only just read this post. I’m not a police officer, just an ordinary member of the public but want to thank you for your post – it should be required reading for every citizen. British police are the best in the world. No person or organisation gets it 100pc right 100pc of the time but I think you’ve shown the brilliance and commitment to your vocation that should make ever office proud and should make every citizen support you.

    Liked by 1 person

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