As mentioned on the “Scent” page, every person has a unique scent. Likewise, the decomposition process releases its own distinctive scent in the form of particles, gases and fluids. This scent is carried by the air currents and ground moisture that are constantly present in the environment and are spread about.
The gases from a buried body will usually percolate up through the soil, while an elevated body will have scent below it from the surface particles that have fallen off.
The Human Remains Detection (HRD) K9/handler team 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.
The team will attempt to find an area on the downwind side of the area to be searched, which will have been based on the investigation to this point.
The handler will decide upon a strategy to locate the scent cone. Depending on the weather conditions, the cone can be relatively small and concentrated, or very large but more diffuse. If there is little air movement in the environment, the cone will coalesce into more of a scent pool that will surround the body.
Every handler has their preferred method, which can include techniques like working a grid, working in from the perimeter, segmenting the area into smaller pieces, or quartering across the wind. They will adapt the strategy based upon the terrain conditions and the weather at the time of the search.
Starting an Area
Some handlers prefer to work their K9 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 dog already s familiar with the scent of human decomposition and usually does not require a scent article.
Working The Scent Cone or Pool
HRD (often called “cadaver”) dogs 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 there’s very little breeze, but the terrain is fairly open so the handler has decided to work a grid pattern. They start the K9 at a location just outside and downwind 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 the scent of human decomposition. Getting to the end of that pass, the handler moves the dog maybe 30 feet upwind, then passes all the way across the search area again while watching the dog’s body language.
The handler repeats this pattern, moving a little upwind each time until the dog indicates they have found an edge of the scent pool or the entire area has been covered as well as possible and the dog has not indicated any scent in the area.
Once the scent pool is discovered, some handlers will continue the grid, working in a smaller area or the K9 will work their way further into the scent pool.
Source of the Scent Pool
When the dog arrives at the point within the scent pool 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. The location automatically becomes a potential crime scene, so the K9 and handler will back out of the area, disturbing as little potential evidence as possible. The location will be marked and the information will be relayed back to the Incident Command Post.
If the missing person is there, the Incident Recovery Team can begin their work.
However, maybe nothing is apparent, but the dog insists there is scent present. Maybe the scent is coming from a buried source, or the scent is coming from blood or other decomposition fluids that have seeped into the surface. Maybe the body was here but has 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.