For starters...............
Originally written on 7th June 2008
Article by Dr Rosemary Claire Taylor MA MB BChir (Cantab)
Olfaction, the act or process of smelling, is the primary special sense possessed by dogs. A dog’s sense of smell is a thousand times more sensitive than humans. Dogs have more than 220 million olfactory receptors in their nose, whereas humans only have 5 million. Specially trained dogs have been used to locate forensic cadaver material and disaster survivors. Highly trained dogs assisted the emergency services in the aftermath of the terrorist attack on the World Trade Centre on September 11th, 2001.
Cadaver dogs need to undergo rigorous training. Prior to beginning a specialised training programme, these dogs need to have basic obedience skills. The cue a dog uses to indicate forensic material depends on the trainer. Some dogs are trained to bark to indicate cadavers, whereas others scratch at the area in the crime scene. Dogs are given a verbal cue to start searching, and directional cues such as “check it out” to indicate an area requiring a more detailed search.
A variety of breeds can be trained to hunt forensic material. Bloodhounds, springer spaniels and labradors are commonly used. Trained cadaver dogs have the ability to detect decomposing bodies beneath running water, for example when a corpse is weighted down, and placed at the bottom of a river.
I have done a thorough search of academic journals on this subject, and will present my findings as follows:
1. Cadaver dogs are known as valuable forensic tools in crime scene investigations. Scientific research attempting to verify their value is largely lacking, specifically for scents associated with the early postmortem interval. The aim of our investigation was the comparative evaluation of the reliability, accuracy, and specificity of three cadaver dogs belonging to the Hamburg State Police in the detection of scents during the early postmortem interval.
Carpet squares were used as an odor transporting media after they had been contaminated with the scent of two recently deceased bodies (bodies are all less than 3 hours old). The contamination occurred for 2 min as well as 10 min without any direct contact between the carpet and the corpse. Comparative searches by the dogs were performed over a time period of 65 days (10 min contamination) and 35 days (2 min contamination).
The results of this study indicate that the well-trained cadaver dog is an outstanding tool for crime scene investigation displaying excellent sensitivity (75-100), specificity (91-100), and having a positive predictive value (90-100), negative predictive value (90-100) as well as accuracy (92-100).
Reference:
Cadaver dogs–a study on detection of contaminated carpet squares.
Oesterhelweg L, Kröber S, Rottmann K, Willhöft J, Braun C, Thies N, Püschel K, Silkenath J, Gehl A.
Institute of Legal Medicine, University Medical Center Hamburg, Germany.
Notes on the scientific terminology in this study;
Sensitivity means the number of correct detections out of 100. Here, all dogs managed to correctly identify 75-100 carpet squares out of 100. This is a good success rate.
Specificity describes the number of false identifications. A sensitivity of 91 out of 100 means, at most, there are 9 false positives in a sample of 100 uncontaminated squares. This is a good specificity, much higher than cervical screening, which can detect far more false positives.
The Positive Predictive Value can be defined as;
In other words, out of 100, there are 75-100 true positives, and 0-9 false positives. A positive predictive value describes the percentage chance, if a sample is contaminated, that the dog will discover it. The value of 90-100 means that, out of 100 contaminated squares, at least 90 are correctly identified by the dog.
The Negative Predictive Value can be defined as;
In other words, out of 100, there are 0-9 false positives and 0-25 false negatives. A negative predictive value describes the chance that, if a sample is not contaminated, the dog will correctly identify the sample as clear of human remains. The study quotes a negative predictive value of 90-100. This means only 0-10 ‘clean’ squares are wrongly identified as contaminated by the dogs.
Accuracy is the degree to which the evidence presented by the dogs matches known information about which squares were marked. The accuracy of dog detection is presented as 92-100. This means that dogs correctly identify carpet squares as ‘marked’ or ‘unmarked’ in at least 92 cases out of 100. This is an impressive accuracy score.
In addition, I think it is important to consider that this is an experiment, not real life. In reality cadaver dogs are given more time to assess possible traces of human remains. Hence in a true police setting, cadaver dogs are more likely to give accurate information.
2. Specially trained air scent detection canines (Canis familiaris) are commonly used by law enforcement to detect narcotics, explosives or contraband, and by fire investigators to detect the presence of accelerants. Dogs are also used by police, military, and civilian groups to locate lost or missing persons, as well as victims of natural or mass disasters. A further subspecialty is “cadaver” searching, or the use of canines to locate buried or concealed human remains.
Recent forensic investigations in central Alberta demonstrated that the use of cadaver dogs could be expanded to include locating partial, scattered human remains dispersed by repeated animal scavenging. Eight dog-and-handler teams participated in a two-month training program using human and animal remains in various stages of decay as scent sources. Ten blind field tests were then conducted which simulated actual search conditions. Recovery rates ranged between 57% and 100%, indicating that properly trained cadaver dogs can make significant contributions in the location and recovery of scattered human remains.
Reference:
J Forensic Sci. 1999 Mar;44(2):405-8.
The use of cadaver dogs in locating scattered, scavenged human remains: preliminary field test results. Komar D.
Department of Anthropology, University of Alberta, Edmonton, Canada.
This study was written in 1999. Nonetheless, in situations where there are scattered human remains, dogs identify them in 57-100% of cases.
3. The detection of human remains that have been deliberately buried to escape detection is a problem for law enforcement. Sometimes the cadaver dog and handler teams are successful, while other times law enforcement and cadaver dog teams are frustrated in their search. Five field trials tested the ability of four cadaver dog and handler teams to detect buried human remains.
Human and animal remains were buried in various forested areas during the summer months near Tuscaloosa, Alabama. The remains ranged in decomposition from fresh to skeletonised. Cadaver dogs detected with varying success: buried human remains at different stages of decomposition, buried human remains at different depths, and buried decomposed human and animal remains.
The results from these trials showed that some cadaver dogs were able to locate skeletonised remains buried at a significant depth. Fresh and skeletonised remains were found equally by the cadaver dogs along with some caveats. Dog handlers affected the reliability of the cadaver dog results. Observations and videotape of the cadaver dogs during field trials showed that they were reliable in finding buried human remains.
Reference:
J Forensic Sci. 2003 May;48(3):617-21.
Cadaver dog and handler team capabilities in the recovery of buried human remains in the southeastern United States.Lasseter AE, Jacobi KP, Farley R, Hensel L.
Department of Anthropology, University of Alabama, Tuscaloosa, AL 35487-0210, USA.
This is an impressive study. The salient points are that cadaver dogs can identify a corpse, or a piece of a corpse, which had been buried at a significant depth. This gives the dog handlers an opportunity to investigate a more ‘real life’ crime scene. Following a murder, it is normal for a criminal to hide any human remains, often by burying the corpse. It appears that these dogs can still detect the ‘smell of death’, when a body part is buried deep in a forest.
- See more at:
http://dogsdontlie.com/main/2008/12/cadaver-dogs-how-reliable-are-they-at-detecting-death/#sthash.1xx3kVVt.dpuf
