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Electronic Noses: Sniffing Out Corpses

13 Oct

When someone is reported missing and it is assumed that they’ve been murdered and dumped somewhere, it is critical for the police to locate the body, since this often gives them the critical clues that they need to determine who the killer was. There may be biological evidence associated with the body such as saliva or semen or blood or skin tissue under the victim’s fingernails. There might be hair or clothing fibers from the attacker. He might have left a fingerprint on the victim’s purse or belt or windbreaker or some other surface that would accept and hold prints.

Finding the body is critical.

The current Drew Peterson case comes to mind. The fact that his most recent wife disappeared and her body has yet to be found is greatly complicating the police investigation into her disappearance. And what about the other Peterson–Scott? Had the bodies of Laci and the unborn Conner not risen from the watery grave Scott gave them, he just might have gotten away with murder. Finding the bodies brought closure to the later Peterson case and hopefully will someday do the same for the former.

How are bodies located?

Let’s say that a young woman walks or jogs through a park or a wooded area on a regular basis and one day disappears while on one of these walks. The police would search that entire area, assuming that if the attack took place on that trail, the body would likely be left somewhere near that path.

First the police would spread out along the trail to see if the body was left nearby. If this was a murder of passion or of opportunity, the killer might not have a plan for body transport and disposal so he would want to get rid of the corpse as quickly as possible. That means he likely dumped or buried the corpse near where the attack took place. So, the best place to look would be near the trail—particularly on the downhill side. Dead bodies seem to weigh a lot more than the person did when they were alive (not true just seems that way) and carrying a dead body uphill is not easy. Downhill works much better.

Investigators would look for disturbances in the ground or interruptions in the normal vegetation that might reveal a recently dug grave. Freshly turned dirt, trenches, or elevations or depressions in the terrain might be helpful. Fresh graves tend to be elevated above the surrounding area, while older ones might be depressed. This is due to settling of the soil, decay of the body, and collapse of the skeleton. Interestingly, the depth of the depression is greater if the body is deeply buried. This is likely due to the larger amount of “turned” dirt, which is subject to a greater degree of settling and the increased weight of the dirt over the corpse, causing earlier and more complete skeletal collapse. This leads to a deeper depression in the soil.

If the corpse has been buried for a number of weeks or months, changes in the natural flora of the area might be seen. Decomposing bodies tend to make good fertilizer and often the flowers and shrubs that grow near the burial site will be fuller and more lush than those in surrounding areas. Often aerial reconnaissance from a plane or helicopter can uncover this. In addition, the plane could be equipped with infrared and other thermal devices that look for heat signals. Freshly turned dirt tends to lose heat more rapidly than does compacted soil so that thermal scanning might turn up a “cold spot.” On the other hand, an actively decomposing body tends to produce heat as one of the byproducts of decomposition and this might be visible on an infrared scanner as a “hot spot.” So any variation from the background level of heat found by thermal scanning should be investigated by searchers on the ground.

Other scanning devices are also used. Ground penetrating radar and side scanning sonar can often be used to locate bodies. In a fairly fresh grave, the soil is looser, less compacted. In addition, a decomposing body tends to add moisture to the soil. These types of scanners can often detect this loosened and/or more moist soil and thus locate the grave. Also, a simple metal detector might locate jewelry, belt buckles, cell phones, watches, or other metallic objects that the victim had on her at the time of burial.

A magnetometer is a device that looks at the magnetic properties of soil. In many areas, the soil contains small amounts of iron, which gives it a low level of magnetic reaction. Since the body itself has a lower magnetic reactivity than the soil, the magnetometer can sometimes detect this variation and help locate buried corpses.

Dogs play an important in corpse location.

Bloodhounds or other tracking dogs might be useful in that they can often track the victim from her home, along the trail, and then to the dump or burial site. Some bloodhounds have even tracked corpses that were transported short distances in automobiles.

Cadaver dogs might be brought in. These dogs are specially trained to sniff out the chemicals of decomposition. When a body decays it releases certain chemicals and these dogs are trained to locate them. They can find a body that is only a day or two old and in some cases ones that have been buried for 20 years. The reason is that the gaseous molecules that are produced during the decay process tend to hang around in the soil for a long time and are slowly released into the air. Though humans might not be able to detect the odor, a well-trained cadaver dog can.

But the days of these detective dogs just might be numbered.

More recently scientists have begun developing what is known as an Artificial Nose, Electronic Nose, or E-Nose. This is simply a device that detects the chemicals of decomposition as they are released into the air around a dump or burial site. It works on the same basis that a cadaver dog does. The released chemical molecules strike specialized receptors within the dog’s nose and if he is trained to recognize these chemicals he will alert his handler to that fact. The electronic nose has sensors that detect the same chemicals.

Many of these devices are simply small portable gas chromatographs, which can separate and identify many chemicals and in some cases determine the amounts of each. Newer studies are looking into using the new technology of microfluidics and LOCAD— Lab On A Chip. These are a spinoff of current research going on at NASA’s Marshall Space Flight Center in Alabama and other areas around the country.

Other uses of such an Electronic Nose would be to detect harmful environmental chemical contaminants, screen for bioterrorism toxins, and maybe even complement fingerprints and DNA as a method for identification. Sort of an Odor Print.

 

8 responses to “Electronic Noses: Sniffing Out Corpses

  1. Pat Browning

    October 13, 2009 at 1:05 pm

    Off topic, and I apologize , but mention of Scott Peterson reminded me — he was convicted but I was never convinced he was guilty. I am not a believer in circumsrtantial evidence, so I was never convinced that O.J. was guilty either. In both cases, maybe the defendants were guilty, but it was never proved to me. I may be the only person in the world who still doubts, but I do.

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    • D.P. Lyle, MD

      October 13, 2009 at 6:58 pm

      There are two kinds of evidence–Direct and Circumstantial. Direct is a confession or an eye witness. All else is circumstantial–things like DNA, fingerprints, blood analysis, toxicology, etc. Since direct evidence is often unreliable–false confessions and inexact witnesses—circumstantial evidence is much stronger and more reliable. Scott Peterson put himself at the scene of the body disposal and was incredibly stupid in his post-crime behavior and there was enough evidence to convict OJ many times over. Both are as guilty as homemade sin–Scott was convicted and OJ reaped the benefits of jury nullification. Fortunately his incredible arrogance led him into an armed robbery in Vegas and they closed the door on him—for a while anyway. Both are where they need to be.

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  2. Pat Browning

    October 13, 2009 at 7:14 pm

    Well, I can see we disagree, but you did clear up the term “circumstantial evidence.” I always assumed it meant things like absence of a body. I associate it with not being able to aliibi yourself because you were in bed reading all evening and all by yourself, no phone calls, no TV, just in bed with a good book, or sleeping. There was an old case in Calif. where a husband was convicted but his wife’s body was not found. My memory is hazy. It was a long time ago, but I think the only “evidence” anyone found that she was dead was a pair of sunglasses.

    The law, like forensics, never fails to fascinate.

    Pat Browning

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    • D.P. Lyle, MD

      October 13, 2009 at 7:19 pm

      Circumstantial means that the judge or jury must interpret the evidence and apply it to the circumstance. If a man’s fingerprints are found at the scene of a murder it means he was there as some time. It is up to the jury to decide if he had an innocent reason for his print to be there or not. Maybe he knew the victim and was in the house often. Maybe he had done some repair work there a week or two earlier. Or maybe he said he didn’t know the victim and swore he had never been there. The jury must then decide if the fingerprint is an understandable and innocent finding or one that points the finger in his direction. That’s circumstantial evidence.

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  3. Margaret Carroll

    October 14, 2009 at 5:21 am

    Wonderful post on e-noses – thank you! Very fascinating. On the topic of O.J. and Scott Petersen – – there is a term that is used in law that I learned a million years ago in a college philosophy course and I can never remember it. Basically, with regard to murder, it means the person with most motive probably did the deed. Is this Occam’s Razor?

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    • D.P. Lyle, MD

      October 14, 2009 at 9:05 am

      Occam’s Razor basically says that if you have two theories that propose exactly the same answer, the simpler one is the right one. In murder, 90+% of the time the killer and victim know each other. Stranger killings are not common. So for some unknown stranger to have come and taken Laci and then dumped her body 100 miles away at the same location that Scott had been fishing on that day defies logic. Possible? Sure. Likely? Not on this planet.

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  4. Joya Fields

    October 16, 2009 at 5:26 pm

    Interesting stuff, thanks for sharing. It’s kind of sad that some police dogs will be replaced by machines, though. I never knew that the dogs were trained to smell the chemicals released by decomposing bodies. I thought they just sniffed out the smell of humans. And the fact that a decomposing body adds moisture to the soil? I had no idea! Thanks for the great information!

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    • D.P. Lyle, MD

      October 17, 2009 at 9:24 am

      Two points: That’s how we all smell–it is contact of molecules released from the object—a corpse or a cheeseburger or perfume or anything—with receptors in our nose that we recognize as odor. We have a memory bank of odors and we call on these to ID the odor. The sense of smell is the oldest sense we have and the most visceral. Odors bring back memories deeper and faster than any of our other senses. Since all the cells in our body as basically water filled bags of chemicals, the human body is almost all water. About 60-70% of the body is water.

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