The CSI death dogs: Sniffing Out the Truth Behind Crime Scene Canines

By Laura Spinney | Wednesday, 28 May 2008

At the former children's home at Haut de la Garenne in Jersey, a sensational discovery was made in February; a fragment of what might have been human bone. It was unearthed by a dog trained to detect human remains.

Forensic experts have pored over it, but the fragment is very small, and with no DNA to go on, it has been difficult to establish whether it is animal or vegetable. On its identity rests not only the question of whether an abuse inquiry is now a murder inquiry, but also the credibility of the policeman's best friend, the sniffer dog.

Dogs' sense of smell is far more acute than that of humans – the nose of a German shepherd contains about 200 million olfactory cells, while a human nose has about 20 million. This superior canine sense has been put to use in criminal investigations for centuries. Dogs used in law enforcement today have an impressive range of skills, from sniffing out explosives to locating earthquake survivors – as in recent weeks in China – and matching criminal suspects to their scent trails – but the speciality in the spotlight in Jersey is the human cadaver dog.

The case has led to some criticism of the faith that police place in these dogs. Nobody really knows how they do it. The dogs don't always get it right, yet the police regard them as a valuable search-tool, to be used alongside other, more scientific techniques such as ground-penetrating radar and aerial photography.

One of the questions surrounding human cadaver dogs is how soon after death they can recognise a corpse, and how long a "fresh" corpse must remain in one place for a dog to detect that it has been there. In a study published last year, the forensic pathologist Lars Oesterhelweg, then at the University of Bern in Switzerland, and colleagues tested the ability of three Hamburg State Police cadaver dogs to pick out – of a line-up of six new carpet squares – the one that had been exposed for no more than 10 minutes to a recently deceased person.

Several squares had been placed beneath a clothed corpse within three hours of death, when some organs and many cells of the human body are still functioning. Over the next month, the dogs did hundreds of trials in which they signalled the contaminated square with 98 per cent accuracy, falling to 94 per cent when the square had been in contact with the corpse for only two minutes. The research concluded that cadaver dogs were an "outstanding tool" for crime-scene investigation.

But how good are dogs at detecting a skeleton from which all the flesh has fallen away? The anthropologist Keith Jacobi of the University of Alabama has investigated this at a police-dog training facility, where human remains ranging from fresh to skeletonised have been buried (the remains were bequeathed by donors).

In one study involving four dogs and their handlers, Jacobi says the dogs were able to detect remains at all stages of decomposition. Performance varied between dogs, but some could locate skeletonised remains buried in an area of 300ft by 150ft. "The few single human vertebrae I used in the study were well over 25 years old, and dry bone," Jacobi says. "This made the discovery of one of these vertebrae, which we buried in dense woods 2ft deep, by a cadaver dog pretty remarkable."

A trained human cadaver dog will not signal a living person or an animal (except pigs), but it will signal a recently deceased, putrefying or skeletonised human corpse. That suggests that the "bouquet of death" is discernible, but attempts to identify it have so far failed. Two of the by-products of decomposition, putrescine and cadaverine, have been bottled and are commercially available as dog training aids. But they are also present in all decaying organic material, and in human saliva.

A human cadaver dog's detection skills depend greatly on its training, and the problem is that human remains are hard to come by. Trainers often use a combination of available "pseudoscents", and pigs. The problem with pseudoscents, says Mick Swindells, a retired police handler who works as a freelance trainer and handler in Blackpool, is that they represent a "snapshot" of death. As decomposition proceeds, the chemistry of the corpse evolves, causing its odour to change. "I'm trying to train a dog to find the whole video, not just a snapshot," he says. Pigs decompose in similarly to humans, and when buried they disturb the ground in a similar way.

A number of research groups are searching for a more precise chemical signature of death. One approach is the "head space" technique perfumers use to identify the components of a scent in order to recreate it in the lab. In this case, small amounts of gas are collected from samples of dead flesh, or from soil in which remains have been buried. The volatile organic compounds given off by the dead flesh are analysed, using a method called gas chromatography-mass spectrometry, to identify their components. Once the compounds are identified, they can be used to make synthetic training tools for dogs or for building machines to detect these compounds.

Swindells says: "The best thing about using a dog to detect cadavers, as opposed to machines, is that dogs have the ability to think. But that's also the worst thing about using dogs." This means that cadaver dogs appear to have sufficient intelligence to recognize a corpse across a range of environmental conditions. However, they can also be distracted, for example by methane produced naturally in a peat bog (corpses also produce methane).

In 2000, freelance dog handler Mick Swindells and his Border collie Shep, a trained human cadaver dog, were called to a 15-acre field near Nottingham to help locate the suspected grave of a murder victim. Shep signalled in one spot and the surrounding area was quickly dug, but nothing was found. Later that day, police returned with an informant, who identified the grave. Shep had been out by a metre.

It transpired that, in digging the grave, the murderer had put his spade through a field drain, causing volatile compounds from the decomposing cadaver to enter the drain. About a metre downhill of the cadaver, the drain was broken, preventing those compounds from dispersing further. The drain had, in effect, separated the body from its scent, and Shep had signalled the dislodged source of that scent – the breakage in the drain.

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Analysis - For some questions, you will be asked to cite the paragraph where the answer can be found.

1. What is the main point of the article?

a. dogs are useful tools for solving crimes
b. bodies decompose in a specific and predictable way
c. dogs must be trained in a specific way to solve crimes
d. there are limitations to what dogs can do for police

2. The article lists several uses for dogs in law enforcement, which one of the following is NOT specifically mentioned in the article.
a. locating earthquake survivors
b. detecting explosives
c. finding drugs
d. matching suspects to scent trails

3. What animal decomposes in the same way as a human? Place a box around this paragraph.
a. cow     b. pig      c. horse       d. mouse

4. What is the “head-space” technique? Place a check mark at this paragraph .
a. a way to recreate a scent in a lab
b. the method by which dogs are trained to detect corpses
c. how researchers dispose of bodies
d. the specific way corpses decompose

5. How are the chemicals of a decaying body identified?
a. reverse osmosis b. filtration
c. gas chromatography d. the head space technique

6. Carpet squares were used in tests to discover what ? Place an X on the paragraph that discusses this experiment.
a. how long a corpse had to be present before a dog could detect it
b. if buried or submerged corpses could be detected
c. how large of an area could a dog cover in a search
d. how accurate dogs were for corpses that had been dead for a long period

7. Why did the border collie (Shep) hit on the wrong spot? Place a triangle at this paragraph.
a. the body had been moved
b. the chemicals from the body had moved through a drain
c. Shep became distracted by a peat bog
d. There were two bodies in the area

8. Why is using pseudoscents, like those of a pig or synthetic compounds not ideal for training? Underline the sentence that answers this question.
a. the scents are very different from human remains
b. the smell of decay changes with time
c. these scents do not last as long as the real thing
d. pseudoscents can be dangerous and illegal

There are several bold words in the article that you can guess the meaning of based on the context. Write your own definition or explanation of each of these words:

9. ACUTE ________________________________________

10. CONTAMINATED _______________________________

11. SKELETONISED _______________________________

12. DISCERNIBLE _________________________________

13. SUFFICIENT ___________________________________

14. TRANSPIRED __________________________________

15. Choose TWO of the words and use them in a sentence.