A vital aspect of a forensic investigation may be to detect and locate specific people or substances of interest, ranging from illegal drugs to missing people to clandestine graves. Sophisticated detection equipment does exist, however this technology can often be expensive, have unsuitable portability, and may even prove useless when searching vast areas. Fortunately for investigators, there is an ideal tool available.
Dogs, sometimes known as K9s or sniffer dogs by law enforcement professionals, have played an important role in legal investigations for decades, with their keen sense of smell being harnessed to aid investigations. The average human being has roughly five million sensitive cells within the nose to aid in scent detection. This appears to be a large number, until compared with the 200 million cells in the average dog’s nose. Further increasing the canine’s sense of smell is an organ in the roof of the mouth that is not present in humans. This organ essentially allows the dog to ‘taste’ a smell, thus strengthening its ability to detect odours. Canines detect odours directly from the source or residual scents; odours which persist in an area after the original source is no longer present.
Obviously the air is full of a vast variety of different odours, many of which will be powerfully clear to the dog. Fortunately they are able to distinguish between different odours, even if one smell overpowers another, and trace a specific scent to its source.
The police commonly train canines to detect the presence of illicit substances to the extent that they are capable of locating even the tiniest trace of a drug. Such dogs are frequently trailed through train stations, airports, country borders, workplaces, and even schools to allow police to locate individuals who are carrying these illegal substances. The dog may be moved near pieces of luggage, near groups of people, or generally kept in the vicinity to react if he or she picks up on an odour of interest. An average stop and search conducted by officers may yield nothing, especially if the subject has hidden the drugs somewhere on his person. However properly trained canines are usually able to detect the scent of illegal narcotics, regardless of where the suspect has concealed them.
Perhaps used more in recent years due to the increased focus on terrorism, canines have also been trained in the detection of explosive materials. The dogs are trained to detect the odours of specific substances such as sulphur, nitroglycerin, and any other compound commonly used in the production of gunpowder and explosive devices. Such specially trained dogs may be used in airports to detect or at least deter terrorism, or in the homes of suspected bomb-makers to identify the presence of these substances on work surfaces and in storage areas. In these scenarios, it is particularly vital that the canine is trained not to touch any substances or devices it does locate, as many types of bomb can potentially explode if touched.
Similar to canines trained to detect explosives, arson dogs are instructed to detect the chemical traces of accelerants. During an arson investigation, one of the primary tasks is to determine what caused the fire and, if accelerants were used, establish where the accelerant was placed. Though the odour of most forms of accelerant is generally quite strong, a fire scene will often be engulfed by the smell of smoke and various burning materials. However dogs can be trained to pick out the specific odours of flammable substances and locate the source. Even if the accelerant is found in numerous locations, the dog can be trained to pinpoint the area in which the accelerant concentration is at its greatest.
Also known as decomposition or victim recovery dogs, these specially trained canines are trained to follow the scent of decomposing flesh in order to locate the bodies of deceased human beings. Whether the cadaver is on the surface, buried underground or under water, a dog’s nose is powerful enough to pick up the scent and trace it back to its source. Cadaver dogs can not only locate actual human remains, but also the location in which a corpse or body parts may have previously been stored by tracking down residual scents. Depending on the use of the cadaver dog, they will be trained to detect specific decomposition odours. For example, some may be trained to detect odours associated with the early stages of decomposition, whereas others may be required to locate older remains. Some dogs are specifically trained to detect dead bodies underwater, with the canine situated on a shoreline or boat. A newer concept is that of historical human remains detection dogs, which are trained to locate historical or archaeological graves.
Search & Rescue Dogs
Like cadaver dogs, search and rescue canines are trained to specifically locate human beings. However in this instance, they are searching for living individuals, usually missing people, individuals lost in the wilderness, and those trapped during mass disasters. For example, trained dogs will be used in the case of an earthquake, where numerous people may be trapped inside crushed buildings or similar. The dogs follow the scent of each person, so that they may be located and finally rescued.
Tracking dogs are trained for the same purpose as search and rescue dogs – they track down and locate living human beings. However in this case the dogs are trained and used to track down fugitives or suspected criminals. The scene of a recent crime may hold the scent of the perpetrator which, if investigators work quickly enough, may be tracked by a trained dog. Alternatively an object or a piece of clothing known to have belonged to or been touched by the suspect may be presented to the dog, hopefully allowing him or her to follow the scent and locate the suspect.
Dogs are trained as trailing dogs and air-scenting dogs. Trailing dogs follow a scent on the ground, whereas air-scenting dogs must be able to pick an odour out of a breeze and follow it back to its source.
Training begins with repeatedly presenting particular odours to the dog whilst teaching him or her to display a particular alert when detecting the odour. The procedure essentially involves typical Pavlovian conditioning. The dog is motivated to perform a particular task and rewarded upon completion of this task. The canine will soon learn to associate a particular act, in this case locating a specific odour, with receiving a reward, generally in the form of food or a dog treat. Throughout the procedure, trainers may use actual samples of what the dogs are being trained to follow, or they may use chemicals which simulate the scent. Initially the dog may be trained in laboratory-like conditions, in which he or she is simply being taught to identify the odours. Once the dog is capable of doing this, scenario-based training may be given. Potentially distracting odours will also be introduced, generally scents that the dog is likely to encounter during a real search. The dog is trained to ignore these odours and focus on specific scents. Upon locating the desired odour, the canine is taught to situate the point at which the source is at its strongest, at which point it will give a specific indication to the handler.
Various breeds of canine are suitable for police work, though golden retrievers, Labrador retrievers, German shepherds, and border collies are all commonly used.
During actual field work, the canine’s handler must aid the dog in any way possible. This includes utilising any known information plus his or her own experience to develop a search plan that will give the dog the best opportunity to locate the desired odours. Allowing a dog to randomly move around and sniff a huge area may yield no results or it will take an extremely long time for the dog to locate the target of the search. In outdoor areas, odours may drift and pool in lower areas or up against physical barriers, therefore these locations should especially be searched.
Every search area should be treated as a potential crime scene. Accurate records must be kept of the entire search, including the trainers and canines involved, the area covered by the search, and any findings. Dogs should be trained in such a way that, if they do locate, for example, a human cadaver, they do not actually touch or attempt to retrieve the remains, which would compromise potential evidence. If anything of interest is found, the appropriate professionals will enter the scene to take over. If nothing is found, the area is deemed as having been ‘cleared’ and the search team can move on.
Stejskal, S. M. 2013. Death, Decomposition, and Detector Dogs: From Science to Scene. Boca Raton, FloridaL CRC Press.