Within a crime scene, the presence and location of blood can provide vital evidence to forensic investigators as to what has happened. We are all familiar with the use of Luminol, a chemical which when sprayed onto a surface contaminated with blood, will react and show as bright blue under ultraviolet light.
While sniffer dogs are most known for detecting drugs and hunting for people both dead and alive, new research is highlighting how the power of their nose is now being used to not only detect the presence of fresh blood but blood which may have significantly aged at an old crime scene.
In a review of the scientific literature on the use of dogs as odour detectors by the Swedish University of Agricultural Sciences, the range of odours dogs have been trained to detect accurately is evident. Within crime, investigation dogs have been used to detect accelerants in cases of arson, explosives, narcotics, and human remains.
The World Trade Center attacks in 2001 prompted the use of trained sniffer dogs in search and rescue efforts, a practice that has been expanded and continued ever since. With smoldering buildings for example filled with smoke once a fire has been distinguished, using a dog can provide fire-fighters with extra assurance that they have not missed a person inside the building through their visual searches, very much hampered by the excessive smoke still present.
Australian researchers from the Centre for Forensic Science at the University of Technology Sydney have now completed studies using specially trained crime scene sniffer dogs reporting success in training dogs to detect both fresh blood and degraded blood. They have found these dogs are able to detect the presence of blood at a crime scene that is up to six months old.
During the investigation of a crime, the more time that passes the more degraded blood at a crime scene will become. As blood is exposed to air its chemical composition changes which affect the odour which is omitted. Blood at a crime scene could be small spots or large spatters, blood that has soaked into a carpet, rug or clothing, or blood which may be on a hard surface such as wood. Small quantities of blood can be easily missed by the naked eye and blood which has been cleaned up is even more difficult to detect.
Often these dogs can also be used to narrow down an area when the exact scene of the crime is unknown. Luminol as a method to detect blood is very effective, however, it can only highlight the presence of blood where the chemical has been sprayed and when the area in question is totally blacked out and ultraviolet light is used.
Luminol is not a fool-proof method. While it reacts with the hemoglobin present in blood to cause the glowing reaction, it can also react with other substances giving a false positive result. Using Luminol in open air environments is not possible with no way to make the area dark and use the ultraviolet light. Furthermore, the use of Luminol means adding a chemical to the crime scene itself which may affect other evidence in the same area.
One of the huge advantages of using a search detection dog is dogs search by smell and not by what they can see like humans do. As highlighted by Search Dogs UK, “Dogs search 3 dimensionally whereas humans only search 2 dimensionally”. Simply put, dogs are able to find traces of blood in areas humans are likely to miss and the early detection of this blood can have significant impacts on a criminal investigation.
A study in 2002 by the Alabama Department of Mental Health and the Auburn University Department of Psychology examined a dog’s ability to learn and detect multiple odours. Through a series of testing, dogs were introduced to a new odour and trained to detect that odour. After 10 days they were given refresher training on that odour before a second odour was introduced and the cycle repeated.
Researchers were interested in how additional target odours affected the dogs’ accuracy in detecting previously learned odours. What they found was that dogs could accurately learn and detect up to 10 odours without any decrease in their accuracy of detection. This demonstrates the ability of trained detection dogs to store, recognize and find multiple odours, alerting their handlers who can then take action.
In the Australian study published in the Journal of Analytical and Bioanalytical Chemistry in September 2016, researchers were aware that scent detection dogs are often used at crime scenes many months after the crime has taken place and therefore any blood evidence present would have degraded over the passage of time. From a scent point of view, this means that the odours emitted from fresh blood samples up to a few hours old will be quite different from the odours emitted from blood that has been openly degrading for months. By training a detection dog to identify the odours from blood at various different stages of decomposition and alert their handlers to their presence, valuable information can be gained which may have otherwise been missed.
The DNA Project reported in 2015 that specialist bodily fluid detection dogs have been used successfully in South Africa for some time to help solve crimes. They report that these dogs were used in almost 2,300 searches across 2015 with just over 700 blood or semen samples found leading to the arrest of 215 suspects. Making use of the natural abilities of dogs and their powerful sense of smell within crime scene investigation and specifically in blood detection, highlights the progress of science and how that science can be successfully applied to aid forensic investigation and solving crimes.