CSI Finance: Every Contact Leaves a Trace (Locard’s Principle)9 min read

CSI Finance - Cashflow Cop Police Financial Independence
(no. 054) – Image Credit: ar130405 (fingerprint) and Markus Spiske (digital background)

It turns out, I’ve accidentally started a mini-series of blog posts where I relate certain elements of policing to money.  They range from some of the ideas in books recommended to me by Police Commanders or general policing principles:

  1. My Stone of Life: Lessons from the Chimp Paradox
  2. Financial freedom by making decisions like a Police Commander
  3. How to Apply a Detective’s Mindset to Protect Your Money
  4. Do you have the Financial Grit to Retire Early?

Today, I’m going to see if I can link a vital concept which underpins forensic crime scene investigations to financial independence.

Let’s call it CSI Finance and the crime of unintentional spending.  


CSI Finance: Locard’s Principle

Some of you may have heard of theory: “every contact leaves a trace”.  It was pioneered by the French criminologist Edmun Locard (1877-1966) and formally known as Locard’s Exchange Principle.

The principle goes like this: the perpetrator of a crime will bring something into a crime scene and leave with something from it, and either can be used as forensic evidence against the perpetrator.

The idea is wonderfully expressed by Paul Kirk (1) 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.

This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.”


Crime Scene – The Unintentional Mind

Offence: Unintentional Spending, Section 1, Financial Independence Act 2019

‘A person is guilty of unintentional spending if he or she –

a) spends, or exchanges – 

i) money, or

ii) any other financial instrument, or 

iii) other property (tangible or intangible), and

b) the expenditure or exchange was done – 

i) thoughtlessly, or

ii) recklessly, or

iii) without care, or

iv) unintentionally, and

c) resulted in a material loss in net-worth in the – 

i) present, or

ii) future”

There is nothing wrong with buying a new car – if it can be afforded and done with proper thought.  There is nothing wrong with buying a coffee everyday, so long as it is done intentionally and properly budgeted for.  

The crime occurs when spending is done unintentionally.  The effect of this is stealing from your present and future self.  It’s the spur of the moment purchases.  The 2-for-1 deals in the supermarket, the Amazon prime deals on a robotic lawn mower which you didn’t think you needed until you saw it on a supposedly ‘limited time’ deal. 

One of the outcomes is such an unintentional mindset is to fall foul to lifestyle inflation.

If you don’t like people tress-passing into your home and steal your belongings, why do you allow yourself to commit an act of self-financial-harm through unintentional spending? 


Exhibit A – The Present You

Every unintentional spend leaves a trace.  The first trace is in the bank balance; money spent not budgeted for means less money to spend on things that were budgeted for.  

The result?  When you don’t want to reduce the budget to take into account the unintentional spending, you end up spending more and risk getting into debt spiral.  Those rolling credit cards, the bank overdraft which never gets paid and continues to creep upwards. 

The promise of tomorrow, next week or next month will somehow be different.  That you will stick to the budget somehow provides the illusion that you’re in control, when in fact, you’ve lost it.  

I say all this because I’ve been there. 

I say to myself every single bloody year that I’m not going to look at Black Friday deals, but always end up doing it until recently.  Last year was the first year I didn’t unintentionally buy something on Black Friday.  I can’t promise I can repeat it again this year, but I will try my hardest to.  

Perhaps setting a reminder to re-read this post on the day will help give me the extra nudge I need.


Exhibit B – The Future You

The second trace is long-term effect on your net-worth.  You might be well versed in the magic of compound interest, but if not it is basically the power of investing a little, early can provide better returns than investing more, later.  

You might have also heard of the term marginal gains. This is wear small incremental improvements when added together can make a significant positive impact.  The opposite is also true.  Marginal losses in this respect are when small accumulated material losses in your net-worth as a result unintentional spending can have a a significant negative impact on your financial wellbeing.  

Unintentional spending can really add up.  By their very nature, they are seldom tracked and aren’t budgeted for.  As a result, it’s difficult to say during a lifetime how much we each spend unintentionally. 

It has been widely cited in different studies that the average person makes over a million in their lifetime, be it dollars, pounds or euros.  I would guess that a majority of the money spent is under the huge category of ‘unintentional spending’.  

Just think of how much your financial independence stash would improve by if some of that unintentional spending was invested?  How many years closer can you get to the state of work optional?   Could you potentially retire much earlier?


Exhibit C – Future Generations

The third trace that left if in the young, impressionable people we interact with.  Whether or not we choose to have children is a personal choice.  But I worry about the example we set for our future generations.

Children learn from adults.  As a parent, I am constantly amazed at what my boys pick up, especially my two year-old.  There are some things which I haven’t taught him, but somehow he has learnt them. 

He now understands that when we go shopping, before I leave the store, I need to pull out by bank card to tap on the machine and pay.  He will throw a full-blown tantrum if I don’t let him do the tapping.  If he can pick these things up at two years old, he will undoubtedly learn how to spend unintentionally if that is how I choose to spend.  

If my children grow up with bad spending habits, there is a good chance I need to look in the mirror before I start to judge them. 


Exhibit D – The Environment

Another trace that is left behind as a result of our unintentional spending is the damage to the environment.  I worry about the rate at which we as a species are consuming and producing.  There is just so much waste and crap that is produced. 

Just take a quick look on Ebay, Amazon or pretty much anywhere.  Plastic garbage that is constantly being peddled which nobody knew they wanted until they saw it.  I’m not even going to provide examples in the small chance it might actually tempt someone who reads this.

Once we are able to collectively reduce our unintentional spending, impulse purchases and spur of the moment splashes, then I think we stand a better chance of not utterly destroying this planet for future generations. 

I’m responsible just as much as anyone else. 

Just a quick look around my house and I can see so many things that will eventually end up in landfill or slowly make its way to pollute our oceans.  

People will stop producing junk when we stop buying junk.

Agent Smith - Cashflow Cop Police Financial Independence
Agent Smith – Image Credit: The Matrix (1999), Warner Bros

Agent Smith: I’d like to share a revelation that I’ve had during my time here. It came to me when I tried to classify your species and I realised that you’re not actually mammals.

Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment but you humans do not. You move to an area and you multiply and multiply until every natural resource is consumed and the only way you can survive is to spread to another area.

There is another organism on this planet that follows the same pattern. Do you know what it is? A virus. Human beings are a disease, a cancer of this planet. 

– The Matrix Movie (1999)

I don’t think we are individually as bad as Agent Smith makes out, but collectively, he has a point.  It’s also one of my favourite films so now was a perfect excuse to include a quote!


Final thoughts

This was meant to a tongue in cheek sort of post but with some serious undertones.  I hope it can help give you a pause for thought before you make your next purchase.  Are you being intentional about your spending? 

I’m not talking here about going through your expenditure like some sort of forensic accountant.  I’m saying maybe it’s time we all shift away from spending so mindlessly.  

Not only does this financially impact your present and future self, but there are wider implications on how any children you have develop their own relationships with money, our future generations and the environment.  

Go out there and be intentional one purchase at a time.  



(A) I must give credit to former Chief Superintendent John Sutherland whose powerful TED talk linking Locard’s principle to relationships provided me with the inspiration for this post.  An incredible writer and well-regarded former Police Commander.  

(B) I’m going to experiment with some shorter style posts like this one every so often.  I enjoy writing the longer ones, but find it increasingly difficult to get the time to do the amount of research that’s needed.

(C) I got the promotion I spoke about – never give up!



(1) Crime investigation: physical evidence and the police laboratory. Interscience Publishers, Inc.: New York, 1953


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3 thoughts on “CSI Finance: Every Contact Leaves a Trace (Locard’s Principle)

  1. Mac_Donald Reply

    (C) I got the promotion and the dream job I spoke about – never give up!

    I’m confused. So you’re now a professional pilot police chef inspector…?

    • Cashflow Cop Post author

      You’re right; that sentence was confusing so I’ve amended it. I meant a specific job within the Police.

  2. Pingback: The Full English – The Crowdfunded Bubble – The FIRE Shrink

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