While we live, we all have a distinct scent, an olfactory profile we share with no one else. But when we die, we ultimately all smell the same.
At a forested area on the outskirts of Sydney – the kind of place someone might dump a body in a shallow grave – a team of scientists is on a quest to isolate and identify the myriad chemical compounds that make up that smell.
If they can work out how the chemical compounds in odours emanating from a rotting corpse change over time and how they interact with each other, they can establish a “scent” profile of a decomposing human body that can be used in forensic investigations.
The work being done in this outdoor laboratory by University of Technology, Sydney (UTS) Professor Shari Forbes and her team of PhD students from the School of Chemistry and Forensic Science could have huge policing implications.
Professor Forbes hopes her work will improve training for sniffer dogs – or scent-detection dogs as they are formally known – and provide scientific evidence about how the dogs detect and locate a scent, which will ultimately increase their success in the field.
"Once a complete chemical profile has been identified, we will then develop scientific-based training materials and aids that can be used by cadaver dog handlers worldwide to help them rapidly and accurately locate human remains,” says Professor Forbes.
The research is vital to the Police’s ability to refine dog training aids, and even dog breeding programs, says Senior Sergeant Dave Wright, NSW Police Training Coordinator for the Dog Development Unit.
“It all comes down to science,” says Sergeant Wright. “It is Shari’s understanding of the chemical signatures of things such as human blood and bone that helps us train the dogs to locate the kinds of evidence we are looking for in the field,” says Sergeant Wright.
“You are talking about a broad range of odours that the dogs are asked to search for, from recently deceased people to skeletal remains; a range of odours in a range of locations which require different search techniques; from drops of blood in a house to bodies dumped in a national park.”
Because approval has not been granted for the use of human bodies, the UTS team carry out their olfactory investigations on pig carcasses sourced from a Sydney abattoir (No pigs are bred for the research program). The carcases are placed on the ground or buried to mimic the characteristics of a clandestine grave.
The researchers visit the facility most days to observe the degree of decomposition, measure the environmental variables such as temperature, wind, rainfall and scents emanating from nearby vegetation, and to capture the odours arising from the carcasses.
A stainless steel hood is placed over a carcass, trapping the decomposition odour. A sample is drawn from a vent at the top of the hood and captured on specially-designed tubes, and then analysed using a gas chromatography–mass spectrometry instrument.
“We collect samples most days, over multiple carcasses and over gravesites to see if the scent is coming up through the soil,” says Professor Forbes. “The odour profile between decomposing pigs and humans is similar although we haven’t yet validated that sufficiently for the Police to use pig carcasses to train their dogs.
“Instead they use human blood, decomposition fluid, grave soil, teeth or bones, as training aids.
“We are testing each of the aids to determine how accurately they represent [the scent] of human remains. Does blood give a similar scent as that from a whole body? Does bone give off the same scent?”
For the Police, knowing if there is a common factor in, for example, fresh blood, blood from a dead person or different blood groups will help them refine training for the dogs.
“There really isn’t much evidence to explain how our dogs detect and locate scents,” says Sergeant Wright. “Tracking down an offender is one thing but a murder investigation could go before a supreme court and the evidence will be looked at very, very closely.”