Cadaver Dogs as a Forensic Tool: An Analysis of Prior Studies

       
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Abstract: This paper discusses studies involving cadaver dog training and cadaver dog accuracy and also discuss the value of using the cadaver dog as a forensic tool.

Introduction

Dogs have established themselves prominently in the law enforcement community. In spite of this, cadaver dogs "have been minimally represented in the law enforcement canine population across the United States" [1]. Cadaver dogs are also known as human remains detector dogs [1], forensic search dogs, and decomposition dogs [2]. The term "cadaver" can be misleading because the dog may not always locate an actual body, but may indicate on scavenged parts, body fluids, or the residual odor of a body [3]. For the purpose of this paper, the term "cadaver dog" will mean any dog trained to detect deceased humans, human parts, or residue from human remains.

The odors emitted by a deceased person begin the moment biological death occurs and are not immediately noticeable by humans. The odors are, however, discernable by dogs. Odors associated with dead bodies differ from one individual to the next even though the process of decomposition and the chemical reactions that occur in humans are generally the same [4]. Unlike the drug detector dog which may have to learn only four to six different odors or the explosives detector dog which must learn nine to fourteen different odors, the cadaver dog is exposed to as many as 424 different volatile chemicals producing specific odors [5]. Exactly which odors the dog alerts on during a search is unknown [6].

Rebmann et al. [4] describe five basic stages and characteristics of human decomposition. During the first stage (the fresh stage), there is little change visible by humans; some dogs may even approach these bodies as though they were alive. However, at this stage, internal decomposition is beginning. In the second stage (the bloated stage), gas is produced within the body, causing it to swell. An odor of decay is present that is detectable by both a human and a dog. Entomological activity may be present at this stage. During the third stage (the decay stage), the gases have escaped the body, exposed skin color changes to a dark or black appearance, and a strong putrefaction odor is present. The fourth stage (the liquefaction stage) occurs as the body begins to dry. The odor produced reduces in intensity, but may become musty. (Galloway classifies this as the skeletonization stage even though body fluids may still be present [7].) Finally, the last stage (the skeletal stage or extreme decomposition) involves most of the remaining flesh drying to the point of mummification. The musty odor remains but is not as strong, and the distance to which it is detectable is much less than in the prior stages. All of these stages provide many odors that the cadaver dog must be capable of detecting.

Several variables contribute to the decaying process and influence the rate of decomposition. Our bodies contain microorganisms that are essential to life, but also play a role after death [4]. Environmental conditions play an essential role in the rapidity of decomposition as well. The location of the body (e.g., water, swamp, desert, depth of burial) influences the rate of decomposition. According to Bass [8], rapid decomposition "can only occur under the most favorable conditions of high temperatures and humidity, ample insect infestation, and the body shaded from direct sunlight".

Training the Cadaver Dog

A suitable dog candidate must be obtained before any training for cadaver detection can begin. All candidates should receive a medical evaluation including radiographs of the hips and elbows to ensure that the dog is structurally sound and is free of disease [4]. The breed of the dog is not as important as its ability to perform the desired task. Its maturity level is important; a dog that is still in the puppy stage will have shorter attention spans, making training difficult. The normal age range to initiate training is eighteen months to four years [9].

There are certain character traits that a dog should have to be able to perform successfully. These traits apply to any dog for consideration in any detection work, not just cadaver work, because the basics of scent detection are the same. A detector dog is searching for something hidden and must have the desire and stamina to search for long periods without giving up. Many trainers categorize these behaviors as drives, often defined as subconscious impulses to various stimulations. Therefore, prey drive would be defined as the drive to hunt and kill something seen as a prey. Another is hunt drive, the drive to search for something. Other drives include air scent, retrieve, play, and activity, all positive factors for a detector dog candidate [9, 10]. Others dispute the use of the word drives in defining dog behavior, preferring to submit substitute labels like character or predisposition [11]. However, in this writer’s opinion, it is simply a matter of semantics.

After selecting the candidate, the training process commences. Here again, we cross into the realm of disagreements. It is sometimes said that the only thing two dog trainers can agree upon is what a third dog trainer is doing wrong. In order to prevent endorsing any particular training method, we will consider the first phase of training termed by Rebmann et al. [4] as imprinting or teaching the dog the odors that it needs to locate.

There are two basic methods of teaching a dog the odors. One method uses actual cadaver material (e.g., blood, hair, or skin tissue) at various stages of decomposition. The other method uses pseudo scents. (The product Sigma Pseudo is available to begin training dogs on cadaver scents without using the genuine item. There are three different products: Corpse I, for simulating a recently deceased body; Corpse II, for the stage of post-putrefaction; and Pseudo drowned-victim scent, to imitate the odor of a drowned body.) Other natural items that can be used include soil from a location recently occupied by a cadaver and adipocere, a by-product caused by decomposition [4].

Dogs demonstrate a particular behavior when the odor for which they are trained to find is located. Some handlers prefer an aggressive indication, believing the dog will work toward a more exact location, whereas others prefer a passive indication to prevent disturbing any forensic evidence. Both techniques have advantages and disadvantages. Each agency should determine the type of indication it would prefer and have its cadaver dog teams trained accordingly.

Behavior of Scent

Whether a dog is searching for narcotics, explosives, a live person, or a cadaver, scent is what the dog uses to find its quarry. Scent will have a propensity to pool around the source and, without outside interference, it will slowly spread. When wind becomes a factor, scent distributes away from the source in the shape of a cone. A high wind will produce a narrow cone, and a slight wind will produce a wide cone [4]. Temperature is also a factor in the behavior of scent. We often base our estimation of the outside temperature by looking at a thermometer, but studies conducted in southern England demonstrated that outside temperature can vary from ground level to one inch above ground level by as much as 17 °F. This same experiment showed a further 14 °F reduction at 12 inches above ground level [12].

There are many other factors that affect scent. Terrain causes variation in the direction that scent flows, which will affect how a dog may indicate on the substance sought [12]. Underground water flows can absorb scent from a buried cadaver and transmit it to a remote location before it surfaces. Likewise, scent from a body under water may not ascend straight up; it may follow the flow of the water and surface from several feet to a great distance from the source [4]. Even the source of the odor will determine its strength. Pearsall and Verbruggen state, “The ability of compounds to give off odor is inversely proportional to their boiling point: the lower the boiling point, the more odorous the substance.” [13] Handlers must be aware of these circumstances to understand why their dogs might indicate on certain locations.

Accuracy of Cadaver Dogs

Although empirical data on the accuracy of cadaver dogs in the field is negligible, some studies have briefly examined the topic. Komar [14] states that most material published on the subject consists of anecdotal reports in nonrefereed journals. In an attempt to bring data that is more accurate to the forefront, Komar conducted studies with cadaver dogs to find scattered remains. The material used as scent sources (hides) in her study varied from human bone, animal bone, sterile gauze or cotton soaked in human decompositional fluid, and small articles and clothing saturated in decay fluids, then dried. There were no artificial scents or pseudo products used in her research.

Komar’s experiments took place during the winter months in Alberta, Canada. Locations of hides placed for the teams to find varied from open fields and plowed fields to wooded areas with dense brush. The articles used were placed 24 to 48 hours prior to the searches. Some of the searches took place in snow, an attempt that some trainers believed to be difficult for the dog. However, Komar’s research demonstrated that the dogs worked well in the snow, burying their noses deep in the snow as they searched. The handler’s reports suggested that the dogs used air pockets within the snow to help locate the articles. Overall, the results were positive with an average success rate of 85%, higher for the more experienced dogs.

An analysis of searches documented over a five-year period in northern New England also revealed positive results. Sorg et al. [6] reviewed the results of 41 searches occurring between 1991 and 1996. Their searches were broken down into three types. The first type involved locations where human remains had already been discovered. The remaining two types were (1) a specific area (due to prior investigative actions) and (2) a nonspecific area (a broad, undefined perimeter based on investigative information). Twelve of the 41 searches involved areas where human remains had already been located. The dogs were deployed in an effort to recover additional remains in which they were successful in six of the twelve searches. Twenty-nine of the searches fell under the latter two categories involving eleven missing persons. Of these twenty-nine searches for the eleven missing persons, the cadaver dogs located three bodies, a human searcher checking an area outside of the dog search perimeter located one, and seven persons remain missing.

The research of Sorg et al. also logged training exercises conducted where human remains had been previously located. The postmortem intervals ranged from approximately 15 days to 72 months. The dogs responded with positive alerts at correct locations 83% of the time. The authors note that in areas where the dogs displayed interest, but did not alert, no human remains were located.

In a drastic change of environment, Lasseter et al. [15] conducted experiments with cadaver dogs in the southeastern part of the United States, specifically Tuscaloosa, Alabama. The purpose of the research focused on cadaver dog performance in hotter, more humid, climates. Varieties of samples deployed in the study included fresh human samples, human skeletal samples, fresh animal samples, and animal skeletons. The purpose of the inclusion of animal remains was to determine whether the detector dogs could distinguish animal from human remains.

There were four dog teams used in the study by Lasseter et al. that had a variety of training and experience. All but one of the teams had certifications in cadaver detection. The research revealed 30% of the alerts given by the dogs were directly on the substance’s precise location, a narrowed location providing a general area, or the dog alerted, but the handler did not recognize the alert. “The term ‘narrowed area’ means that the dog and handler team accurately felt that the remains were in an area in which the remains were situated, but the handlers were not able to specifically identify the exact location.” [15] The higher percentage of positive alerts occurred on skeletal remains rather than fresh remains. All dogs gave false alerts (alerting where no substance was placed) during the trials. This occurred mostly in the first trial. Nervousness about the test on the part of the handlers possibly contributed to this behavior.

Previous research by France et al. [16] indicates a dog’s effectiveness decreases as the temperature exceeds 85 °F. It was possible for the source of the scent to be located, but only from a closer distance of approximately one meter. It was obvious that heat and high humidity made searching difficult on the teams. Even with frequent breaks and cool water provided, extreme humidity and heat caused the dogs to pant, thereby reducing the accuracy of their search.

It was demonstrated in the study by Lassester et al. that none of the teams distinguished between fresh animal remains and human remains with precise alerts because no direct alerts occurred at any location. When a handler made the narrowed area call, it contained both animal and human remains. The research previously discussed did not document training methodologies, so it is difficult to know whether the teams had worked around animal remains as a distraction, thereby training the dogs not to alert on such material. It is therefore advisable to work detector dogs around a multitude of distraction smells and situations to prevent false alerts.

Conclusion

A properly trained cadaver dog is a valuable asset to the homicide investigator as well as to forensic teams in locating bodies, scattered remains, or residual material. Continued research is necessary to improve our understanding of the detector dog’s behavior, whether based on training philosophies or biological conditions (stress, illness, or fatigue). Only through this type of research can we establish general training guidelines and more accurate cadaver search teams in the future.

For further information, please contact:

Jonathan K. Dorriety
Kaplan University
Chicago, IL
jdorriety@kaplan.edu

References

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Article submitted by the Author
Article posted: December 3, 2011

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