Tuesday, June 5, 2012

Tracking Scent vs. A Decomp Search...What's The Difference?

By Tom Adair; author of The Scent of Fear
I get a lot of questions from folks regarding dog searches so I figured today would be a good day to address one big difference between search methods. There are two basic types of "people" dogs can search for; living or dead. The training is different for both. That's because the "evidence" or scent the dog is searching for is different between living and dead victims. NecroSearch International and it's dog handlers have been investigating this issue for 25 years and other handlers have been going much longer. Dog tracking is an old "art" and we've learned a lot over the years. The one things we don't know with certainty is the exact molecules the dogs rely on most. That's for one simple reason. Dogs can't talk. That's okay though because we still learn a lot from working with well trained dogs and handlers.Each handler trains their dog to give a specific "alert" when they find the scent they are looking for. One famous handler I have known over the years trains his dogs to stop and sit.

When searching for living persons the dog is tracking their unique "scent".  Millions of skin cells are sloughed off every day in our various activities and a well trained dog (like a bloodhound) can tell the difference between each person's "scent". To begin these searches the dog handler will introduce something from the victim (like an article of clothing) for the dog to acquire the scent. This item is called a scent article. A well trained dog may then follow that scent trail (sometimes many miles) to the source or until it becomes too degraded or diffused in the environment. The key aspect of this search is that the dog is searching for a unique "scent" given off only by the one person being searched for.

Searching for a deceased body is an entirely different process. When searching for a deceased person the dog is looking for "decomposing human scent", not the scent given off by a living person. Put simply, this is because the cells are breaking down and decomposing (not vital). This means that knowledgeable investigators would never use a scent article to acclimate the dog. There are several challenges to this type of search. The main problem is that the dog is looking for any decomposing human scent. This means that a dog will alert on any human decomposition fluid or tissue. So in addition to dead bodies they will also alert on things like urination spots, feces, and baby diapers. This is a huge concern in rural areas and trash dumps because investigators may have dozens of "alert" areas to investigate. The scent can persist for months or even years in some cases.

Another very interesting phenomenon is that dogs can not differentiate between the decomposing scent of humans and that of pigs.  Pigs have been used for years as human surrogates in a variety of scientific studies. Pigs have a very similar biochemistry, skin to tissue ratio, and are large (relatively hairless) mammals like people. So if a body is believed to have been buried at a pig farm we have to use other methods to detect the body. This conflict isn't very common but it happens and police need to be aware of the issues surrounding these searches.

If you are writing a scene of a dog search it would be wise to understand the basic difference between these searches. The easiest way to remember is that living persons can be searched for specifically. In those searches your character will need some kind of scent article like a piece of clothing, hairbrush, or bedding (if they sleep alone). If your characters are looking for a dead body they will likely find a lot of red herring alerts. These are frustrating because the dog will give a "positive" hit but excavation of the soil may not reveal anything (such as in the case of public urination). You may be able to use that to your advantage in the story so think of how dozens of these "false hits" may affect morale. There is only so many baby diapers you can dig up before questioning the wisdom of getting out of bed that morning :).

11 comments:

  1. A post after my own heart, Tom.

    My research for RED TIDE included a cold case search with some detectives in Lakewood using a Human Remains Detection dog. It was fascinating to me to see a dog and handler work together. Jamie Taylor, the dog handler in my book also has a Search and Rescue dog and a therapy dog, each with a very different focus.

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  2. Very interesting stuff! And well-timed, as I'm writing a scene that involves a search dog looking for the scene of a crime by searching for the scent of person. Thanks for a great post.

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  3. What breed of dog are you using LJ?

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  4. Interesting! Thanks for sharing, Tom.

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  5. What breed of dog should I use, Tom?

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  6. In my humble opinion there is no better breed than the bloodhound. I have seen them do unthinkable tracks (following vehicles, finding graves under flood waters, etc). Tracking is what that dog was bred for and there is no equal.

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  7. Good to know, Tom. I need to call one of my local law enforcement sources and see what dogs they're using. I've seen pictures of German Shepherds, so I think that may be the case.

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  8. Shepherds are ideal for crowd control, arrest, building searches, things like that, but in my experience they are ineffective at long distance and decomp searches. I've had a number of cases where the first dog on scene was a Shepherd and it either lost the track quickly or didn't pick it up at all. Later a bloodhound showed up and followed it for miles.

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  10. Lots of good information here. Thank you, Tom.

    I have one question: If a person was recently killed, could a tracking dog follow the scent to get close to the body site, from which a decomp dog could finish up? Could save some of the false positives that arise in decomposition searches.

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  11. Yes Dana, dogs can track the "live scent" for days and sometimes weeks depending on weather conditions. In fact, a sad fact is that some of the live tracks end at the dead body. A decomp search is a more localized technique (X marks the spot so to speak) and a scent track can go for miles. Usually a decomp search is conducted in a specific location (field, home, park, etc.)Hope that helps.

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