Dogs trained to find human cadavers are law enforcement’s best option when they need to find a body. But how do dogs sniff through swamps, burned buildings and other places with plenty of distracting odors? It turns out, decaying human bodies have a unique scent signature.

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Now researchers have isolated some of the key chemical compounds that make up the human scent of death, reports Elizabeth Pennisi for Science. The information could help people train cadaver dogs.

While the chemical scent cocktail of a dead human is unique enough that dogs can be trained to find it, some dogs are trained using decaying pig flesh because the smell is similar. The new research isolated eight compounds that are only found in the dead bodies of humans and pigs. Five other compounds are unique to pigs alone.

The researchers, led by analytical chemist Eva Cuypers of the University of Leuven in Belgium, published their work in PLOS One.

Pennisi describes the work:

Cuypers’s graduate student Elien Rosier started by putting tissue samples and organs from six autopsied corpses in jars in a lab closet. The jars’ screw caps, which let in some air, had stoppered holes that allowed her to periodically take samples of the gases building up inside. She set up other jars with pig, mouse, mole, rabbit, turtle, frog, sturgeon, or bird remains. Pig remains in particular have often been used in past decomposition studies because of their similarities to human bodies (which are often hard to come by): They have the same microbes in their guts, the same percentage of body fat, and similar hair as people. But it was not clear whether the decomposition process was the same because the two species had never been studied under identical conditions.

The team found 452 organic compounds in the gases over six months of decomposition.

A researcher not involved in the work, points out that isolating tissues in jars means that Cuypers and her colleagues may not be getting the whole picture. The entire body is likely to have a complex bouquet and pieces of it may be missing from the analysis. And that researcher would know, he’s Arpad Vass and works at the University of Tennessee, Knoxville, Body Farm, a facility where researchers study decomposition by observing real bodies as they decay in different weather and other conditions — whether buried or submerged in water or left in the open air. It’s one of several body farms in the U.S.

But Cuypers has thought of those questions. “The next step in our research is to see whether the same compounds are found in buried, full decomposing bodies in the field and to see whether dogs trained on the mixture respond more specific[ally] to human decomposing bodies," she tells Science. Ultimately, the knowledge may mean that an electronic nose will replace Fido’s nose.

Yet canine senses will be hard to beat. In October 2013, a man was convicted of murdering his wife even when law enforcement couldn’t find a body, reports Liz Lucking for The Guardian. Cadaver dogs were able to pick up the faint scent of human remains on a rug the man buried.