Forensic scientist makes scents of sniffer dog wizardry

Shari Forbes is digging up the dead animals she buried months ago in a secret forest clearing in the Blue Mountains north of Sydney. The forensic scientist bottles the odours of rotting flesh and bone to take back to her laboratory to build a chemical profile of the around 800 active compounds involved in decomposition odours.

Professor Forbes is a world expert on the smell of putrefaction and her regular digs are inching us closer to understanding how sniffer dogs find things. Cadaver-detection dogs help find bodies in police investigations or after natural disasters. They locate their quarry by homing in on just a few of those 800 compounds in decomposition scent.

If we knew which ones they focused on, we could synthesise them and use them to train sniffer dogs and speed up their work. Ultimately, the data could be fed into what is called an electronic nose and some of the basic functions of a cadaver dog could be automated. 

“It’s not my intention to put the dogs out of business,” Forbes said. “If we brought the electronic noses out, we’d use them as a screening tool. We would still use the dog as the confirmatory tool.”

A dog’s sense of smell is a thousand times better than a human’s. And even a human’s sense of smell is hundreds of times better than the very latest electronic nose.  Forbes is still amazed at how good dogs are at smelling death.  “I test them and they recognise a decomposition odour,” she said. “I take that same sample back to the lab and my instrument tells me there’s nothing there. So we know the dogs are better. And they will be for a long time to come.”

In life, we all smell different; in death, we all smell the same. But there are different smells at different stages of decomposition. Cadaver dogs surely know this but what the dogs smell is probably not what we smell.

To us, putrefaction smells universally bad. But to dogs, there are gradations and distinctions. These are still hidden from us.

 “The other issue with odours is that when you change the ratio of the compounds, that changes the odour,” Forbes said. “So we could have two identical compounds in different ratios giving off two different odours.”

Dogs are absolute magic because they will not be fooled by different ratios in compounds. Will we ever get instrumentation as good at the job as they are? “Probably never,” Forbes said.

Animal carcasses are used to collect smells because genetically they are very close to humans. Working on corpses, banned in Australia, is permitted in the United States. Forbes visits there every year to see how close animals and humans are.

 “There are some minor differences which could in fact be the compounds that the dogs recognise as human decomposition,” she said.

Forbes helps train cadaver dogs and is called on to help in criminal investigations. She was drawn to what has become her vocation by a police request years ago.

 “They were out looking for a grave and the dogs were trying to locate it,” she explained. “The police said ‘we really don’t know what the dogs are doing’ and I thought ‘I could help with that. I know the chemistry behind the odour. They know the dogs’ behaviour. We can tie this together.’”

Her expertise has been called on to help police find drugs, weapons, cash and explosives. She has also helped police find a dead cadaver dog, because they thought it would be too upsetting for all involved to set a live dog to find a fallen comrade. Dogs can be trained to detect anything; all that is needed is the substance and to train them on it. If it were possible to isolate a likely selection of the active compounds that Forbes reckons the dogs home in on, the dogs themselves could be set the task of picking the right ones.

 “What we can do is improve their success rate by screening away all the interfering background odours and just present them with the target odour and say ‘Is this what we’re looking for?’ When presented with those odours, they have phenomenal success and that’s really the aim.” — DPA