Cadaver Dogs -- A study on detection of contaminated carpet squares

Cadaver Dogs – A study on detection of contaminated carpet squares L. Oesterhelweg, S. Kröber, K. Rottmann, J. Willhöft, C. Braun, N. Thies, K. Püschel, J. Silkenath, A. Gehl Forensic Science International 174 (2008), p A presentation by Karen S. Garvin ANTH398F, Spring 2008

Dogs have a very sensitive sense of smell and are able to discriminate among many odors. Specially trained dogs have been used in law enforcement agencies and rescue operations to help find criminals, sniff out bombs and drugs, rescue individuals, and locate dead and missing persons. Search dogs that are trained to find the scents associated with death are called “cadaver dogs.” These cadaver dogs are considered to be valuable “forensic tools” when they are part of a trained dog/handler team.

One purpose of this paper was to discover how soon after death a cadaver dog might be able to discern the scents associated with death. In the experiment that the researchers conducted, their test time frame was just under three hours. They re-tested the dogs’ abilities to locate scents on carpet squares up to 65 days after the carpets had been contaminated with chemicals meant to simulate death. For forensic anthropologists, this means that cadaver dogs may be very good at helping to find bodies that are up to several months old. This paper did not address longer time frames.

The aim of the experiment presented in the paper was to investigate the reliability, accuracy, and specificity of three cadaver dogs’ abilities to detect the scents associated with death during a time frame that included several hours after death. Other studies have examined the reliability of search dogs in identifying different types of materials; however, this study focused on the early postmortem interval in an attempt to determine how soon after death a cadaver dog might be able to pick up on a scent.

The experimenters used new carpet squares as an “odor transporting media.” Two corpses, “A” and “B”, were wrapped in blankets to simulate clothing and the carpet squares were placed under their bodies in order to pick up their scent. 24 carpet squares were placed under “A” for 10 minutes during three consecutive sessions. 8 carpet squares were placed under “B” for 2 minutes during two sessions. Then, the carpet squares were put into glass jars and taken to the Hamburg State Police Department’s Police Dog Training Center.

The researchers set up a row of six glass jars, each containing a carpet square. Three cadaver dogs were instructed to search for contaminated carpet squares. Contaminated carpet squares were placed in the jars at irregular intervals; some test runs did not contain any contaminated carpet squares. Neither the dogs nor their handlers observed placement of the carpet squares. The cadaver dogs were tested more than once during a 65-day test period, depending upon the availability of the dog/handler team.

10 Minute Contamination DogBKLTotal Sensitivity Specificity PPV (positive predictive value) NPV (negative predictive value) Accuracy Source: Table 3: Statistic values, 10 min. contamination In this table, the data is given for the three cadaver dogs that were tested on carpet squares that had been contaminated for 10-minute intervals. Dogs “B” and “L” scored 100% accuracy. Dog “K” identified contaminated squares 94% of the time. Overall, the accuracy of all three dogs is 98%.

Because it is not known explicitly what the chemical compounds of death are, no one is quite sure what the dogs are actually smelling. Putrescine and cadaverine are two components of the smell of death, but that is not all. Therefore, the cadaver dogs’ expertise cannot be replaced by instrumental analysis or chemical laboratory techniques at this point in time. The researchers conclude that cadaver dogs are very valuable as part of a forensics investigation team, and should continue to be used as a “forensics tool.” They suggest that the reliability and accuracy of cadaver dogs may be enhanced if two or more dog/handler teams are used independently at the same crime scene and their results compared.

Cover Photo: Tyler, one of the Bay Area Recovery Canines, at work searching a debris pile. Tyler is a Chesapeake Bay Retriever and is owned by Brian Ward. Photograph copyright Heather Roche. My thanks to Brian Ward and Heather Roche for permission to use the photograph of Tyler.