1898 Bloodhound Decision Still Raises Relevant Issues

In the decade before 1900, tracking dogs began to be used to find suspects. The courts of the time struggled with the issues of how and when to admit this kind of testimony, which involved a silent witness not available for cross-examination. A case decided by the Kentucky Court of Appeals in 1898 reversed a conviction of two men accused of burning a barn who had, according to the evidence, fled to a tenement building “occupied by a large number of families and individuals, many of whom were of bad repute.” A dog had tracked to this location, and the testimony of other witnesses led to their conviction.

The dog was a major link in the evidence and the Kentucky appellate court held that the reliability of the dog was not sufficiently established. The case was remanded for a new trial. The court noted that bloodhounds had been used in the not too distant past for tracking runaway slaves and were still used to track convicts. A partial concurrence/partial dissent is, in my opinion, even more interesting than the majority opinion in providing an overview of what was changing about the law of dog tracking at the end of the 19th century. I quote the central part of Judge Guffy’s argument:

"I concur in the reversal of the judgment in this case, but dissent from so much of the majority opinion as holds that the trailing or proven trailing of the defendant by a bloodhound can be introduced as evidence upon the trial of such person charged with any crime. It is true that the majority opinion so restricts such proof, and requires so many conditions precedent, that, if the opinion in question should be strictly adhered to, no great injustice would very often result from evidence admitted under the ruling in question. It, however, seems to me, with due respect to the majority opinion, that such a rule of evidence is contrary to all other rules of evidence, and, if not in violation of the letter of the constitution, is manifestly in violation of the spirit, as heretofore expounded by this court. Such a rule seems to me an innovation upon all the heretofore established rules of testimony. The use of bloodhounds was, perhaps, necessary to efficiently and effectually uphold the institution of slavery, as well as to aid in the arrest and capture of persons accused of crime in the Dark Ages. In such cases, however, the object sought was the arrest or capture of known fugitives. If the dog in fact took up and followed the trail of a fugitive, and found him, or aided his pursuers to find him, the object was accomplished, and there could be no mistake as to whether he was the party sought or not; his guilt and right of capture having been theretofore established, and in fact being unquestioned. If the hound took the wrong trail, and brought to bay the wrong party, that fact would be ascertained so soon as the pursuers reached the party, and the utility of the hound in that regard then ceased. It is now proposed to use the hound, not to capture a fugitive, but to ascertain or furnish evidence to convict some citizen of crime. It seems to me that this new use of the bloodhound is a radical departure from the former purposes for which they were used; but, whether this be so or not, it seems to me that neither the life nor liberty of a citizen should be taken away or even jeopardized by the mere fact that some person testified that the hound was well trained to track human beings, etc., and that he had trailed the accused from the scene of the crime to the habitation of the accused, or until he came upon the accused party. There is danger that the effect of the majority opinion will likely be to greatly promote the raising and training of bloodhounds, or hounds that will be called bloodhounds. It is a well-known fact that the owners of hounds, as well as other property, usually hold such property in high esteem; and, as the owner or trainer of hounds will be engaged in the business for pay, it will be greatly to their interest to always have well-trained hounds. In fact, I presume there will be none but trained and expert hounds in a few years; at least such will be the opinion of their owners, for it would be utterly useless to have any other sort. It is common tradition, and doubtless believed by quite a large number of persons, that bloodhounds are capable of wonderful feats of trailing. In fact, the many wonderful stories told of the achievements of bloodhounds (mostly in the imagination of those originating them) have instilled into the minds of quite a number of persons such wonderful notions of the unerring, if not infallible, knowledge and intelligence of the hounds, that the fact that the hound said that a certain person had lately been at the place where the crime was committed would be the most conclusive proof that could be produced."

This kind of skepticism of tracking evidence has remained in the law, perhaps at a higher level than the science now justifies. Pedigo v. Commonwealth, 103 Ky. 41 (1898).

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How Many Footsteps Do Tracking Dogs Need to Determine Direction of a Scent?

A man crosses a football field. Twenty minutes later a tracking dog is brought to the midpoint of the trail and commanded to TRACK. The dog will sniff the area, perhaps back-track a few steps, and then move in the direction that the man walked across the field. How does the dog know which direction the man was moving in? How many footsteps does the dog need to be able to smell to determine the direction the man was walking? Two researchers in Belfast asked these questions and devised an elegant experiment that may have narrowed the possible answers to the first question. As to the second question, the dog cannot reliably tell direction if there are only three steps but it can do so if there are five. Here’s how the experiment was conducted: A dark beige wool carpet was cut into 18-inch squares. Twenty-one squares were lined up and a man walked across them, stepping once on each square. As in the football field, the dogs were brought to the midpoint and told to TRACK. Neither the handler nor the dog had seen the man walking on the squares. The dogs, which had been trained as trackers, reliably went in the direction the man had gone. Two squares were removed so that there were only 19 squares. The dogs were still reliable. Then two more were removed, and so on. The dogs retained their ability to detect the direction of the trail down to five squares, but at three their choice of direction became random. They needed more than three footsteps. Could it be the direction of the footsteps that the dogs used to determine direction? After all, the heel hits before the toe and perhaps this provided a cue. So the researchers mixed up the squares, using a computer program for randomness, but kept the direction of the heel-toe axis of each square facing the same direction as the man had walked. The dogs were not successful in finding the correct direction. They did not seem to be able to rely on general body deposition (the plume of skin flakes, etc.) to determine the direction of the target. The researchers theorized that there is an odor gradient that results from either a stronger smell for more recent tracks that gives the direction to the dog, or alternatively, there is a decay factor which is stronger in the footprints from the direction that the man began at, which the dog used as a signal to move in the opposite direction. The researchers are working on additional experiments to answer more questions about the tracking skills of dogs. D.L. Wells and P.G. Hepper, “Directional Tracking in the Domestic Dog, Canis familiaris,” 84 Applied Animal Behaviour Science 297-305 (2003).

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Scenting Skills Now Part of Genetic Research on Dogs

We shed 30,000 to 40,000 skin flakes each minute. (Picture shows electroni microscope image of a desquamated skin flake, at least a thousand of which you'll shed by the time you finish reading this piece.) Clothing is permeable to this particle stream and it comprises between 70% and 90% of house dust. These skin flakes spread up and out from the body by heat and air currents in a pattern known as a plume, and are a major part of the scent trail that a tracking dog follows. (See Gary S. Settles, “Sniffers: Fluid-Dynamic Sample for Olfactory Trace Detection in Nature and Homeland Security—the 2004 Freeman Scholar Lecture,” 127 Journal of Fluids Engineering 189 (March 2005); Robert Hunt, “The Benefits of Scent Evidence,” FBI Law Enforcement Bulletin, p. 15 (November 1999).) How the olfactory systems of dogs work is a study in itself, as are the fluid dynamics that describe the dissemination of the plume—how far and how quickly it spreads. Dogs can generally find scent trails within 48 hours after the target has been in an area but much longer periods have been reported. An FBI newsletter describes a case where a bloodhound followed a trail from a car abandoned 17 days earlier to a suspect’s apartment building. This dog was even able to follow the 17-day old trail into a commuter station to a kiosk where the suspect caught a bus. The dog was thus able to ignore the scents of thousands if not tens of thousands of commuters in tracking the suspect. (Guy J. Hargreaves, “Detection Dog Lineup,” FBI Law Enforcement Bulletin (January 1996).) Another area of research on dog scenting concerns the dog genome. In 2008, a team of Polish scientists determined that variations in olfactory receptor genes “might affect the olfactory ability of service dogs in different fields of specific substance detection.” Twin dogs with a specific gene variant were able to track better than other dogs with different variants of the gene. (A. Lesniak, M. Walczak, T. Jezierski, M. Sacharczuk, M. Gawkowski, and K. Jaszczak, K., “Canine Olfactory Receptor Gene Polymorphism and Its Relation to Odor Detection Performance by Sniffer Dogs,” 99(5) Journal of Heredity 518-527 (September/October 2008).) Thus, it might soon be possible to predict, both for cancer sniffers and other detection dogs, whether a puppy is a good candidate for such work. It might even be possible to select for genetic predisposition to high tracking skills in breeding programs. Whether that kind of dog breeding will be a good thing I am not sure, but I have no doubt that someone will make it part of a breeding program sooner or later.

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