This review covers a wide variety of forensic anthropological search techniques for human remains and clandestine graves. Clandestine graves are graves that are dug by an unknown person in an unknown location. It is one of the roles of forensic investigators and forensic anthropologists to help identify and locate human remains and these clandestine graves because without the victim’s remains there would be a great deal of unsolved cases. Some suspects may not even see trial because there is no body for police agencies to link them to the crime. There are many techniques that can be used to locate these graves, ranging from older techniques, such as using human remains detection dogs, to newer techniques, such as using decompositional odor analysis. This review aims to look at a wide variety of different forensic anthropological searching techniques and identify how successful each of the techniques are for locating human remains and clandestine graves, and the limitations and problems of each technique. This review is based on the examination of the work of thirty-two articles and books that will cover all the areas of a number of different techniques currently being used in the field. A great majority of the articles are from academic peer reviewed journals, and range from the years 1995 to 2014.
Human remains detection dogs is one of the oldest (1) and reliable techniques for locating human remains and clandestine graves. A dogs’ sense of smell is 1,000 times more sensitive than that of a human (2), which makes human remain detection (HRD) dogs a valuable asset when locating human remains and clandestine graves. But HRD dogs are not always accurate when it comes to locating human remains because they can often give “false alerts.” Although HRD dogs can give false alerts, there are different external factors that can affect a HRD dog’s ability to locating human remains, such as the amount and kind of training the dog has received, weather conditions, the strength of the scent, which might be lowered because there has been a long time since the victim’s death, and other geological and ecological conditions (2). These factors are why HRD dogs undergo extensive training and continue to be tested regularly.
Training of HRD canines is curial to their ability and success out in the field. Lasseter et al.‘s study of Cadaver dog and handler team capabilities in the recovery of buried human remains in the southeastern United States concluded that there needs to be standardization of how human remain detection dogs are trained (3). Not having a set of universal standards to train HRD dogs, hinders the HRD dog’s credibility and reliability of locating human remains. Over the last decade there has been a push for set standardized techniques for training human remain detections dogs. Committees such as the Scientific Working Group for Dogs and Orthogonal Detector Guidelines (SWGDOG) have established what they believe to be the best practice guidelines for HRD dogs (1). SWGDOG consists of experts from local, state, federal and international agencies, who meet to determine these guidelines and explore how this discipline could be improved upon (1).
Along with this push, there have been recent developments to help and test the dog’s accuracy; such developments include using volatile organic compounds (VOCs) to develop tools such as the Scent Transfer Unit (STU-100) (1) to help dogs get a better, stronger scent. VOCs are volatile organic compounds that come from the ground and the area surrounding human remains in a grave (4). They are incredibly useful for helping human remains detection dogs because they can make up whole odor profiles for the dogs to use. What is meant by this is that, when a body is decomposing it undergoes four known stages, Fresh (autolysis), Bloat (putrefaction), Decay (putrefaction and scavenging) and finally Dry (diagenesis or mummification) (5). Recently discovered, it will also release different scents, VOCs, at these stages. By understanding what VOCs are and the ability to provide the scent to the HRD dogs through technologies like the STU-100, dogs will now have a better capability of detecting the scent of human remains no matter what stage of decomposition they are in.
The Scent Transfer Unit is a “dynamic airflow collection device” (1). The STU-100 takes the scent from the sample you want the dog to get the scent from and concentrates it, so they can get a stronger, amplified scent to work from (1). The whole system is made up of a Teflon-coated hood, which holds a gauze pad that collects the concentrated scent from the sample that is attached to a small vacuum pump. The air from the vacuum draws the scent from the sample, to the gauze pad which holds the concentrated VOC, which then can be given to the dog to smell. This device has appeared to be very successful, showing that it has had success rates of 73.5% to 82.2% (1) from studies of it used in the field.
There have been similar studies that have explored the use of VOCs to advance the field in cadaver dogs. There has been research in Decompositional Odor Analysis (DOA) to help canines locate human remains. Currently there has been research done to make a database of Decompositional Odor Analysis Volatile Organic Components. Creating this database has shown, researchers that the odors that come from decomposition changes over time (4). To be able to detect these changes of scents, the researchers have developed different methods and techniques to collect these samples. Such methods include Triple Sorbent Traps and the Spiking method.
The Triple Sorbent Traps (TSTs) are made up of sections of 14mm Carbotrap-C, Carbosieve S-III sorbents that are packed into a stainless steel tube (4). Once the sorbents are placed in the tube, the Triple Sorbent Traps are cleaned by being heated to 380°C for approximately three to four hours long (4). During this process there is a flow of helium that is introduced at 50-100mL/min to further clean them. After the traps are cleaned they are stored in a freezer at -18°C (4). These traps are used by being put into the ground, via the spiking method. The Spiking Method consists of a static dilution process that utilizes 250 mL amber dilution bottles; which are equipped with a screw-on vapor-lock valved cap; which is constantly maintained between 70°C to 90°C during this process (4). The Spiking method and the TSTs are used together to collect the VOCs from the sample area. These methods have produced great results by identifying 30 key makers of human decomposition (4). The discovery of these 30 makers proves to be important because they do not only add to the database of VOCs, but they are all detectable at the surface level of the grave, which makes it ideal for human remain detection dogs. This database is idea for human remains detection dogs because it allows for them to be better trained for remains at whatever decompositional stage.
Not only is technology helping HRD dogs to improve, in action experience is as well. HRD dog trainers and police forces are testing the dog’s abilities in different circumstances by providing different types of training, such as in wildfire recoveries and searching for just human teeth. It is important to test HRD dogs in different circumstances because if there is problem where the dogs are not responding well because they the circumstance is preventing them to do so, the handlers can then train the HRD dogs to be able to respond to that circumstance. It is important to test the HRD dogs for searching areas of the body such as human teeth, because it shows that HRD are reliable for detecting human remains, even when they are locating the smallest of body parts.
Human teeth, are the strongest substance in the human body, they will often withstand extreme heat which makes them incredibly useful for identifying burnt human remains. But human teeth are small and often can be lost when the body is buried, moved or dumped. Training HRD dogs to locate all of the remains will prove advantageous, not only for credibility in the field but for identification purposes. Locating human teeth is not a standard in training HRD dogs and if a dog is to specifically locate human teeth the handler must train their dog to do so (6); this is the difficulty of not having this specific method standardized. The importance of finding teeth for identification purposes is important, and by not having the training could lead to not being able to identify an individual. Although this ability is valuable it is not well tested. There have been very little studies conducted on testing HRD on their ability to locate human teeth. One study done by Cablk et al. tested HRD abilities to locate teeth, but had a very small sample size, only having tested three dogs (6), that had different level of training. With having a small sample size it is hard to test the abilities objectively. Based on this study the dogs scored an 81%, 67% and 65% (6). The study does show that the HRD dogs can locate human teeth, and that with more testing we could get a better understanding of how reliable they can be for locating them.
Locating human teeth could prove very valuable especially in wildfire search and recoveries. Wildfires are naturally occurring fires that tend to be extremely large and have proven to be difficult to manage. They often burn down entire forests, and towns. It is unfortunate that sometime people who are living in these town, happen to be caught in the path of a wildfire, do not get the chance to evacuate and sometime die in these fires which is why HRD dogs are used in wildfire searches. Texas is an area that is prone to wildfires, and because of this they have created a task force, known as the Texas Task Force 1 Urban Search and Rescue (TX-TF1). The TX-TF1 uses HRD dogs to locate victims who were trapped in the way of the wildfire. In September of 2011, Texas was hit with an unsuspected wildfire that rapidly spread throughout Bastrop County. During and after this wildfire the TX-TF1 used HRD dogs in what is believed to be the largest detailed search for human remains (7) searching a final area of 15 598 acres (7) for human remains.
This research provides evidence of the importance and the abilities of HRD dogs in locating human remains. Dogs are one of the best of methods used for locating human remains; they are reliable and prove to have a great deal of success doing it even without the standardization. It is clear from the literature that canines are extremely successful at searching and locating human remains and clandestine graves, with standardization and more testing in areas such as locating human teeth, this technique of searching will only improve.
There are many different ways that technologies have been able to help forensic investigators locate human remains and clandestine graves. These techniques have proven to be extremely useful and successful at locating clandestine graves in different environments. Some of the most successful techniques the literature has indicated are Ground Penetrating Radar, Electrical Resistivity, Time-Lapse Resistivity, Remote Sensing and Probing.
Ground Penetrating Radar (GPR)
Ground Penetrating Radar (GPR) is without doubt the easiest and most used technological based searching technique that used to locate human remains and clandestine graves. GPR is commonly used in archaeological and forensic investigations because the units are portable, accurate, non-invasive, and non-destructive (8, 9). It has been a well-accepted method not only in the archaeology world but for forensic purposes since it was first successfully used in 1986 (9). GPR works by transmitting and reflecting Electromagnetic (EM) wave energy (2). A GPR survey is conducted with two antennas, the first one transmits the EM waves via short pulses into the ground while the other antenna receives the reflected waves (8) which provide a picture of what is going on underneath the surface when viewed on the display panel.
What makes GPR one of the more popular methods to use to locate clandestine graves is that the investigator collects data, from the survey, in real time, which can be displayed on a black & white or coloured screen (10). The investigators immediately know if they have found a possible location of a grave when looking at the real time data. Not only is GPR good for real time data, but it has the best resolution of subsurface features out of all the other geophysical technologies (10, 11). This advantage adds to why GPR is so popular to use to locate clandestine graves. From this real time data and the high resolution, investigators can make preliminary assessments from the field (10), and can start excavations immediately. The size and the depth of the grave can also be measured from the real time data (10) which allows the investigators to have an idea of what they are excavating, and to make sure they do not miss evidence. Finally what makes GPR so useful is that is can be used over concrete, blacktop and fresh water (10). This is advantageous because other methods may or cannot locate graves in these specific areas, but GPR can do this without disrupting the surface.