The case of Garrido, who was arrested in California last month on suspicion of kidnapping an 11 year-old girl and holding her hostage for 18 years, highlights the role of the special canines used by police to locate bodies.Different than Bloodhounds, which focus on a particular scent, cadaver dogs are trained to track a range of decompositional smells. They can locate bodies just hours after death or find ones that have been rotting for 20 years. Police hope the cadaver dogs searching Garrido’s yard will unearth clues to a series of unsolved prostitute murders from the 1990s.
The first dog used exclusively for cadaver work was a yellow lab named Pearl, in 1974, according to the “Cadaver Dog Handbook: forensic training and tactics for the recovery of human remains.” Pearl was trained at a military research station in San Antonio, Texas. Her first assignment was for the New York State Police, who were looking for bodies in an upstate forest. Pearl unearthed the corpse of a Syracuse College student that was buried four feet deep.
Over the next decade, cadavar dogs were intoduced at police forces across the country. Common cadaver dog breeds include German Shephards, Labradors and Golden Retrievers. Both male and female dogs are used, although females in heat are avoided because the hordes of nearby male dogs they would attract could sully a crime scene.
“The most important consideration is drive,” says the Cadaver Dog Handbook. “Basically, you should look for a dog that is ‘ball crazy.'”
The advantage that a dog has over a detective is its superior sense of smell. The brain of a human has approximately 5 million olfactory receptor cells; some dogs have about 100 million.
The smells of death are a result of the decomposition process. Minutes after a person dies, bacteria already within the body begins to decompose it. Cadaver dogs can detect a corpse at this point but humans cannot. In the following hours, the body swells from gases produced through decompistion. As the the body collapses, gas escapes, giving off a putrefying odor that can be detected by dogs and humans. Eventually, the liquids created during the decay process seep out and the body dries, producing a cheesy, musty smell that is also quite detectable. As flesh disappears and the skeleton emerges, a musty odor is emitted. Humans are unlikely to detect a corpse at this point; dogs still can.
Terrain and weather are important in a cadavor dog’s ability to detect scent. Temperatures of between 70 and 100 Farenheit are optimal. At hotter temperatures, bacteria become less productive. Bacteria also need a constant air flow to supply oxygen. Moisture is necessary too but the body itself typically provides it.
Something emitting a strong smell will create a space packed with odor directly above it called a scent pool. Air flow moves the scent away from the source, forming an air scent cone. Secondary scent pools will form at scent barriers, such as a tree standing downwind from a body. Secondary air scent cones spread out from here.
Flowing water can help distribute a scent downstream but water can also interrupt the absorption of a scent into the soil, causing a scent void, which limits a dog’s ability to detect scent.
Cadaver dogs have been applauded by police departments the world over, but they are costly. They need food, shelter and training.
Presently, scientists are working to develop technology that could make cadaver dogs obsolete, or at least give them a run for their corpses.
Researchers at the Oak Ridge National Laboratory, where uranium was purified in World War II, are studying the chemical signatures of decomposition. Their aim is to develop an electronic nose that one day will be able to scan a body and reveal the time of death.
Dan Sykes, a forensic science chemist at the University of Pennsylvania, is also working to engineer an electronic nose. The logistics of acquiring fresh human corpses for research is difficult, so he uses pigs.
“These dogs are highly effective, but it takes a lot of time, money and manpower to train them,” said Sykes, after a recent meeting of the American Chemical Society, in Washington D.C. “A device that is as effective as dogs, but is a fraction of the cost, would be something worth pursuing.”