Evidence Recovery part I
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By SMI Aycock

Evidence recovery is nearly a forgotten art form in the K9 world.  Every year there are an increasing number of dogs being produced and classes being held that do not specifically search for and locate evidence.  In fact, ASCT itself ceased the requirements for evidence recovery on certification a few years ago but has recently decided to add the work back into certification. Why? Because evidence recovery can and does lead to case closings, arrests, and stronger track success.

Years ago, evidence recovery was a staple of police K9 training and street performance.  Prior to narcotic detection becoming such a national requirement and need, evidence recovery was the focus.  The K9 olfactory system allowed the detection of miniscule, hidden, even buried case evidence.  Agencies depended upon dogs abilities to help discover those needed pieces of evidence for a case.

But with the ever increasing demand for more work load on the K9 teams - most K9 schools now have either eliminated the need for evidence recovery or have reduced it so deeply that there is only a fraction of general information offered. 

It’s time to put evidence location back into our K9 team abilities.

For the next couple of months we will dissect and plan the strongest method of evidence recovery.  At the conclusion, the reader should certainly have enough information to not only, understand and train a K9 for the work but also have enough knowledge to explain and teach the process.

So let’s get started.

The first part of evidence recovery is understanding what happens to the scent on a technical level.  This understanding allows us to carry out training in a more realistic view and recognize goals and problems as what they are - and how to troubleshoot the situation before it ever occurs.

In evidence recovery, the scent causes the most problems in the training…this will lay the foundation for what the scent is and how it behaves.


Let’s make this as simple as possible. Here are the rules:

1. There is a specific scent (signature) for each environment. 

If you happen to walk along a roadway and you focus your scent abilities exclusively to the environment, you’ll notice a certain smell.  Now, that smell may be trees, grass, vehicle fumes, asphalt, garbage, decaying road kill, Etc. but the roadside has a smell.  Continue walking and after a distance the smell changes a bit - gradual - but change.  Next, turn and head off into a field and you’ll notice a complete new range of scents.  These changes are what we call signatures.  And, of course, we humans pick up on macro-quantities of scent change where the K9 picks up on micro-quantities.  So where we may walk a mile and notice a few changes, the K9 notices hundreds.

2.  Every object has it’s own scent (chemical specific).

Take a screwdriver, a folding knife, a straight blade knife, a semi-auto handgun, a blue-steel revolver, a wallet, cash, keys, - anything - and smell them all.  Yep, smell them (but don’t let other officers see you do this or you’ll never hear the end of it).  Every type of object has its’ own smell.  Screwdrivers smell the same.  Specific plastics smell the same.  Leather smells the same.  Hard steel smells the same. Etc. The reason for this is that each individual object has a chemical makeup of a specific type.  Those chemicals (or elements themselves when speaking of metals) give off a scent that is the same.
What changes in the scents of the objects is simply what they’re made of.  So if a folding knife has a wooden handle it will smell different than the straight knife made only of steel.  And - there are differences in steel manufacturing and metals that are incorporated in the blades.  This is the same process for nearly all objects of common need.  Go ahead - smell some stuff.           

3.   Objects hold scent

This is a general statement because it is a general application - meaning - objects hold all types of scent
(not just human scent). 

When an object is tossed into an environment (this means any environment - including a cabinet drawer, tool chest, purse, Etc), it assumes to take scent of that environment.  Remember rule #1.  Every environment has a scent and every scent from that environment is a gas expression from a chemical element or property.  That gas clings to objects (bonds).  Therefore, when a wallet is thrown into a ditch, it immediately begins to take on the scent from the environment of the ditch. 

In addition to this environmental scent lock, the rule also applies to human scent (on a grand scale).  And the human scent is easier for the K9 to detect.  Why?  Because human scent is purely organic (except for very few artificial scents) and organic scent (meaning it is comprised from a base of carbon - and carbon causes more residue).  Simply, human scent sticks to things easier.  Since the wallet will hold scent - and human scent sticks to things easier -  human scent will stick to the wallet easy. 

How long will human scent remain on a wallet or knife?  Until it evaporates.  Evaporation is what removes human scent.  The H2O of the human scent compound evaporates and with it goes the other properties that give the human signature (to be discussed in another article).  When the evaporation takes place - the scent is expressed to gas and the scent leaves the bond of the knife.

 4.   Seven days

Once an object is thrown into an environment, it immediately begins to absorb (bond) the scents of the environment.  At ambient (normal, average or room temperatures) temps it takes an object seven days (SEE ASCT EVIDENCE SCENT RESEARCH STUDY 1996) to absorb enough  of the environmental scent to smell exactly like the environment. This is the point when every object in that environment smells the same.  And this is the point when the K9 has trouble picking up on the object as a separate component of the environment.

What happens?  The gasses from the environment envelope the object and bond to a point where the objects original scent is masked with the scent of the environment.  The original scent is still there but it’s underneath all that environmental scent. 

Other than human - the environmental scent that has attached to the object will remain there until the temperature is high enough to cause that scent to change to gas.  Simply, that doesn’t happen unless you live in the HOT southwest USA.  Otherwise, the scent will typically remain on the object until the object is removed from the environment.

Example:  Take a K9 to a relatively clean yard and blind toss a few items, allowing the K9 to scent to them. Then, repeat the same scenario along a roadside where there is a  heavy garbage collection. What you will notice is that the K9 can pick out the scent object from the remainder of junk without any real difficulty.  However, leave that object there for seven days and return for the search. The K9 will have an extreme time recovering it.  Rule 4 is the cause.

5. The softer the material - the better the bond.

Metals typically have an Ionic bond and thus are tighter than softer materials. What this means for us is that the tight bond limits the metal from being porous enough to hold scent as well as...say...the wallet.

Typically, the harder the surface, the less scent will attach to it.  Some will attach - but not as much.  Just as with asphalt limiting the scent during tracks - the same reason applies here to evidence.  

These are the five rules of evidence scent.  These rules are important for our next step of training for evidence recovery.  Try and understand the concepts of the rules.  Trust them, as they are completely accurate and without them you will likely struggle in the live finds for evidence. 

Next time, we’ll start the dog in training.

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