As mentioned on the “Scent” page, every person has a unique scent. When we are alive, we all smell different to the dog.
Conversely, the decomposition process releases its own distinctive odor in the form of particles, gases and fluids. These decomposition products are basically the same for all humans, yet differ from most animal remains. Odor from these products is carried by the air currents and ground moisture that are constantly present in the environment and are spread about.
Human remains release these decomposition products into the environment around them. If there is sufficient air movement these will coalesce into a scent cone, otherwise a scent pool will form and spread around the body. Gases from a buried body can percolate up through the soil, while an elevated body can have scent below it from the surface particles that have fallen off.
The Human Remains Detection (HRD) K9/handler team (often called a “cadaver dog”) takes advantage of this fact to find the scent floating in the air or upon the ground and follow it to the strongest source, which usually is the location of the human remains.
Every handler has their preferred method to try to locate decomposition odor in the area to be searched. This could be working a grid, coiling in from the perimeter, segmenting the area into smaller sections, or quartering across the wind. The handler will decide upon a search strategy based upon the normal behavior of the dog, the terrain in the search area, weather conditions since the person went missing, and other relevant information from the investigation to this point.
Starting an Area
Some handlers prefer to work their dog on-lead to keep them relatively close. Others, unless there is some hazard to working off-lead, like along a busy highway or in an area with steep drops, will work off-lead, allowing the dog to freely range through the area. Depending on the particular situation, a handler may choose either method.
Once the dog is ready, the handler will signal to the dog that it’s time to work by giving it the search command and directing the dog into the search area. The cadaver dog is already familiar with the scent of human decomposition and usually does not require a scent article.
Working The Search Area
HRD dogs often carry their noses up most of the time, occasionally stopping to pick up scent from the ground, the surrounding vegetation, the wall of a building, or anywhere else the scent can collect.
As an example, lets assume the handler has decided to work a grid pattern. They start the K9 at a location at one “corner” of the search area, give the dog the search command and direct them along the “bottom” perimeter of the search area, watching for any change in body language that shows the dog is picking up human decomposition odor. Getting to the end of that pass, the handler moves the dog maybe 30 feet perpendicular to the pass they just made, then moves all the way across the search area again while always watching the dog’s behavior.
The handler repeats this pattern, moving back-and-forth across the search area, until the dog indicates they are detecting odor, or the entire area has been covered as well as possible and the dog has not indicated any scent in the area.
Once scent is discovered, the team will work their way further into the scent pool to locate the source.
Source of the Scent
When the dog arrives at the point within the search area where the scent is the strongest, they will identify the location by performing a “Trained Final Response.” This is a behavior that has been reinforced throughout the dog’s training to indicate to the handler that this is the source of the odor they have been seeking. Remains may or may not be visible to the handler. In most jurisdictions, this location automatically becomes a crime scene, so the location will be marked and the information will be relayed back to the Incident Command Post, after which the K9 and handler will back out of the area, disturbing as little potential evidence as possible and the Incident Recovery Team can begin their work.
However, maybe nothing is visible, but the dog insists there is scent present. Maybe the scent is coming from a buried or elevated source. Maybe scent is coming from blood or other decomposition fluids that have seeped into the surface but the remains themselves have been moved or become disarticulated by animal activity. There are many possibilities, and Law Enforcement will continue their investigation with the marked area as an additional clue.
Additional areas may be attempted and the search will continue until the missing person is located and recovered or the search is suspended until further investigation can provide additional clues with which to work.
Advanced Human Remains Detection
Also sometimes referred to a “Crime Scene” HRD, this level of certification is tested by experienced K9/Handler teams. It typically consists of minute amounts of human remains source placed in scenario-type situations such as blood spatter on a surface, fluids that have been cleaned up, tiny amounts in a vehicle, and so on.