If the technique also works for human remains, it may help law enforcement personnel find hidden graves of victims months after a murder, researchers say. Because the method relies on a superthin, flexible tube to catch faint chemical signatures in air pockets near the corpse, it may be used to detect bodies buried in hard-to-reach areas, such as under concrete slabs.
“There are about 18,000 homicides annually in the United States and 100,000 missing persons, so stuff like this is needed,” says forensic scientist Arpad Vass of Oak Ridge National Laboratory in Tennessee.
Currently, people use corpse-sniffing dogs, ground-penetrating radar, and chemical analyses of air and soil to pinpoint buried bodies. But study coauthor Thomas Bruno of the National Institute of Standards and Technology campus in Boulder, Colo., says that none of these methods would work in every situation.
The new method promises to be specific, sensitive, and importantly, flexible, Bruno says. The tube could be inserted into a small hole drilled into a concrete slab or rubble to sniff out bodies buried underneath. “For a body buried under a concrete slab, there is nothing else that would work,” Bruno says. “Ground-penetrating radar has problems, and you don’t have access to the soil to do analyses.”
As a corpse decomposes, tissues break down, releasing bits of nitrogen-containing compounds into the surrounding soil and air pockets. These compounds are known to react with a chemical called ninhydrin, causing it to change color. A bluish-purple flush signals a decomposing body. (Conveniently, ninhydrin is also used at crime scenes to detect sloughed-off skin tissue in fingerprints.)
This chemical method may be more precise than a cadaver-sniffing dog, Bruno says. “When you get a positive result with a ninhydrin … you can be pretty confident about the compound that produced it. But if you get a positive response from a dog, yeah, there could very well be a cadaver present, but it could also be something else.”
To test their method, Bruno and his colleague Tara Lovestead, also of NIST, built what he called a “little pet cemetery” of rat gravesites. The rats were enclosed in wooden boxes and then either buried under 8 centimeters of soil or left on top of the dirt.
The researchers collected the air around the rats by threading a thin tube through holes in the boxes. Suction at the other end of the tube drew out the air surrounding the corpse. The air samples were then taken to the laboratory and analyzed with ninhydrin.
Bruno and Lovestead detected no ninhydrin-reactive nitrogen in the first month of the experiment. Bruno says that this might be due to slow decomposition in Colorado’s cold weather in May and June, when the experiment began. After five weeks, though, the probe detected strong signals from boxes containing dead rats. Rat-free sites showed very low levels of these compounds. After 20 weeks, six of the eight sites with rats still had detectable levels of ninhydrin-reactive nitrogen.
Chemical analyses of soil involve lots of messy chemical reactions, Bruno says. The new method is “a very neat and clean method that minimizes waste. With this, the wet chemistry is minimized because the sampling method is so much easier.”
Vass points out that the study is just a first step and needs to be validated on buried human remains before it would be useful to agents in the field. “It’s a very nice beginning study,” he says. “I’d like to see this expanded before we get too excited about it.”
Forensic scientist R.E. Gaensslen points out that the technology wouldn’t be helpful for canvassing large areas, but might be used in cases where information points to a particular location. “If you have to search a big area, then it will probably be planes or helicopters and infrared photography or something like that to detect hot spots,” says Gaensslen, of the University of Illinois at Chicago. “If you are searching a relatively confined area, you can potentially use techniques like the one in the article.”
