Can Dogs Smell Blood?

It has been said that dogs are one of the best screening tools in a crime scene search. Dogs are often the first port of call at a crime scene as the area needs to remain unspoilt for as long as possible so that the dogs have the best chance of picking up any scents that may be crucial in solving a crime. It is vital to be able to locate blood at a crime scene as it can help identify suspects and victims, recreate the events that took place, ascertain murder weapons and find the link between an individual and objects/locations.

It’s clear that dogs can smell blood, but let’s look at this in more detail. 

A dog’s natural ability and its highly sensitive sense of smell has enabled the progress of forensic science and solving crimes through blood detection. When a dog smells blood it will sniff or nudge the area, and in the case of being trained, they will also sit down when they have smelled blood that is hidden. 

This kind of detection is far better than any man-made device, as sometimes it is only small volumes of blood that are present. Once the dog has shown the signs of its detection, police authorities are then able to investigate further.

A dog can be trained to give any trigger, but in some cases, a dog will attempt to lick an area with blood, which in personal cases, is fine, but for forensic cases it can tamper with evidence. 

Historically, dogs and their wolf ancestors use blood trails to hunt their injured prey. Since dogs have become domesticated, this instinct has become less pronounced but in some dogs, it comes naturally. 

In recent times, particularly in Europe and Australia, law enforcement agencies have begun using blood detection dogs. These dogs have been purposely trained to seek out blood evidence. This way they have been able to search a large area which could be a potential crime scene related to a missing person, a murder, an assault case or mass disaster. 

These blood detection dogs are a relatively recent unit that come under a bigger group known as ‘detection dogs’ which are used by law enforcement agencies. As dogs have a very sensitive sense of smell, they can pinpoint odors such as explosives, human bodies, drugs and now, also blood.

The aim of forensic odor profiling is to unveil the chemical aspects of odor. Research has focused on single odor-producing elements of blood and looked into how changes in the environment affect the capability of blood detections distinguishing these. Gases which are given off from blood samples are collected and then the gaseous odor molecules are detected individually and identified.

Quite often, these searches take place a long time after a crime has been committed. Studies were conducted which compared the odor of fresh and decomposed blood. This was profiled over two years and given to body detection and blood detection dogs who were in training.

Results seemed to reveal that there is a clear odor change between blood which has been collected within 48 hours to blood which has been decomposed. Remarkably, those dogs that were trained on fresh blood were able to locate blood which was up to six months old and could even locate blood which was up to twenty-four months old.

This research also revealed that where the blood was found also had an effect on the odor that was produced by the blood. Blood which was found on non-porous places (e.g. objects that are metallic) and blood which was found on porous places (e.g. an item of clothing) had a distinctive odour profile pattern.

It is clear that blood detection dogs need to be trained so that they can find blood in any possible crime scene.

Blood donations have also enabled us to understand what human blood smells like. Although human blood tends to smell the same, there are variations which are related to differences in health, diet, lifestyle and other environmental factors. Regardless of this, it has been stated that this does not affect a dog’s ability to be able to find fresh or decomposed blood from different people.

Studies have also compered detecting latent blood (blood which us not visible to the eye) by dogs, when compared with another method e.g. luminol (a chemical used to detect blood.)

An artificial situation was created where a suspect tried to remove blood from a victim by washing a piece of clothing five times. Results revealed that body and blood detection dogs are far more sensitive than existing detection approaches, but they are on par with luminol. 

A sniffer dog or a detection dog is specifically trained to use its senses to be able to detect blood as well as other substances. Smell is the sense that is used most by dogs. Some dogs are better than others at detecting the smell of blood, and sometimes the breed can make a difference, so certain dog breeds are used for certain roles. 

Blood detection dogs do not need to be smart, if anything this can be a negative as it means they are easily distracted. Ideally, the dog needs to be midsized and have a personality which does not get bored or tired of playing will a pull toy or a ball.

The aim is to eventually get the dog to link the smell of blood with the toy it plays with by making the toy smell of blood.

The dog needs to be trained to and be exposed to find blood in all sorts of situations. You need to teach the dog to be able to sit or lie calmly when it finds a scent. If the dog frolics, urinates or digs, it can destroy any potential evidence.