How To Collect and Preserve Scent Evidence
Why go to the trouble of collecting and preserving scent evidence?
(1) Scent evidence is the only evidence which-- when used with a bloodhound trained to discriminate the scent of one person from another-- can lead you from the crime scene to the perpetrator or the victim. In the case of a missing child, there may be multiple crime scenes to preserve–where the child was last known to be, where the child was seen, and where the child sleeps.
(2) A bloodhound’s following a scent trail even a short distance gives grid search teams a direction of travel. Following the path taken may lead to hard evidence being discovered along the flight trail or to potential witnesses. Dropped objects help connect the suspect to the crime scene or to evidence found along the scent trail, such as the weapon thrown in a trash can, a smear of blood on a car. The weapon will have the perpetrator’s scent on it even if he wore gloves. All body fluids give off the unique scent of the person whose fluids they are.
(3) Even if the bloodhound loses the faint scent trail flowing out through the car ventilation system, the dog may lead you to tire marks or foot prints or a security camera which may help you identify the type of car or prove the child was abducted by car so that you can issue an Amber Alert. Of course, if the windows of the car are down, or the child is carried away in the bed of a truck or on a bicycle or in the arms of the predator, the child’s scent trail is easy for any bloodhound trained to trail to follow.
(4) If the scent trail takes you to a residence, this will usually give you probable cause to get a warrant to enter the residence. In advance, law enforcement should check with the state attorney’s office to find out if there are any emergency situations when you may go inside the residence immediately without having to wait outside for a warrant, as, for instance, when there is the suspicion that a child under a certain age has been kidnaped and is being raped or killed.
(5) If a suspect is located and it’s believed that a dropped cigarette or other evidence at the scene or along the scent trail may be his, the bloodhound can be scented on the evidence and pick out which person in the scent lineup, if any, handled the evidence. Before trial, the scent identification of the cigarette can be verified by a DNA comparison of the saliva on the cigarette and the suspect identified by the bloodhound as the person smoking the cigarette.
(6) A bloodhound can place a suspect at the crime scene by identifying which suspect’s scent was collected from the crime scene on a gauze pad. For example, a scent article can be made by wiping where the screen was cut to get into the child’s bedroom. It is kept stored in a zip-lock bag properly labeled as any evidence.
(7) A bloodhound’s picking up or failing to pick up a trail where a suspect says the victim was allows you to verify or contradict the suspect’s story. Pauline Zales initially said she took her child to a swap meet, the child wandered off, and someone must have taken the child. If a bloodhound had been brought in and scented on an article of the child’s clothing, and, then, not been able to find the child’s scent at the swap meet location, the detective in charge would immediately have had reason to suspect her story. It later was proven that she had killed the child and never taken the child to the swap meet.
(8) Scent evidence is admissible in most state courts provided a proper foundation is laid to show that bloodhounds as a breed when properly trained can trail individuals, that is, can scent discriminate one person from another, and that the particular bloodhound who followed the scent trail in this case has reliably trailed in the past. It also must be established, of course, that the scent article was properly collected and preserved. Tomlinson v. State, 129 Fla. 658, 176 So. 543 (Fla. 1937); Edwards v. State, 390 So.2nd 1239 (Fla. 1st DCA 1980).
Is there normally scent evidence at the scene of a crime?
As master bloodhound handler Bill Tolhurst said on page viii of his book Manhunters (1984): “Scent is the one piece of evidence that must be present at the scene of a crime. The criminal may walk on a concrete floor and leave no tracks, wear gloves and leave no fingerprints, but unless the entire area has been burned, he still leaves scent. . . . You can’t see it. You can’t smell it. You can’t photograph it. You can’t dye it. You can’t lift it like a fingerprint. You can’t find it with a laser. You can’t send it to the lab for analysis. But it’s there--just waiting to be used.” Tolhurst later proved that the scent of whoever handled a bomb survives on bomb fragments, despite the high heat generated by the explosion. See his book, The Invisible Witness Scent (2000).
How is scent created?
The human skin consists of over 60 trillion living cells. You are always shedding cells, like an invisible dandruff dropping off around you. According to William Syrotuck, on page 37 of his 1972 book Scent and the Scenting Dog, the human body sheds dead or dying skin cells at the rate of approximately 40,000 every minute. More recent estimates make it millions of cells shed a minute. Whatever the number, your unique scent is produced as a by-product of the bacteria on your skin feeding on your dead and dying cells as they drop off. See page 15 of Milo Pearsall and Hugo Verbruggen’s Scent: Training to Track, Search and Rescue (1982).
What is a scent trail?
Your scent rafts swirling in the air around your body are swept up from your feet to above your head as the air warmed by your body raises. When you step out from under the plume over your head, the air cools, and these scent rafts fall on the weeds, bushes, pavement, even walls of the buildings as you move pass them. The conically shaped pattern of debris left deposited behind you is called your scent trail. Your scent trail is as easy for a properly trained bloodhound to follow as it would be for you to follow footprints left in wet sand.
Does every human being have a different scent?
“Although culture, diet, environment, heredity, and race influence it to some degree, the combination of bacteria, vapor, and cellular debris is believed to be unique to the individual, accounting for the singularity of human scent.” “The Benefits of Scent Evidence,” FBI Law Enforcement Bulletin. Bill Tolhurst, in his book The Invisible Witness Scent (2000), on pages 74-75, documents tests he has run which prove that even identical twins have different scents.
Why are dogs able to smell differences in scent people cannot smell?
Dogs have a lot more olfactory cells in their noses than humans. For example, a sheep dog has 220 million olfactory cells compared to only 6-10 million in the human nose. This enables a sheep dog to smell 44 to 100 times better than a human being. Vroon, Piet, Smell: The Secret Seducer (New York: Farrar, Straus, and Giroux 1994). Because bloodhounds have been able to regularly follow fainter human scent trails than any other breed, it is believed that the breed has more olfactory cells than other breeds. There is some speculation that bloodhounds are engineered for scent trailing, their large ears scooping the scent toward their wet noses where it sticks.
How long will a scent trail remain?
It might remain for weeks or scatter beyond recognition very quickly if the scent rafts are few in number, as they are when coming through the ventilation system of a car. Also, some environmental factors--wind, temperature, humidity, and terrain-- affect how long a good scent trail will stay together. At some point, regardless of how incubating the conditions are, the scent trail will disappear. This is due to the very biological process which beget the scent trail: the bacteria feeding off the dead or dying skin cells complete their feast, eliminate their by-products, and go on to digest other things. So, it’s smart to bring in a well trained, scent-discriminating bloodhound as soon as possible after an abduction of a child occurs.
Why should bringing in a bloodhound be part of the first response when a child is believed to have been abducted?
Because there is always a chance a sexual predator may kill the child he has abducted, bringing in a bloodhound within an hour of the child’s being reported missing gives the child the best chance of being found in time to save his or her life. U.S. Department of Justice statistics show that more than 40 percent of abducted children which are murdered are killed within the first four hours; 90 percent within the first 24 hours. A Washington state study concluded the fuse is even shorter, claiming that 90 percent of the children murdered are killed with the first four hours. Another reason to bring in the bloodhound team upfront is that this increases the chances of catching the sexual predator while he is still with the child. When the kidnaping and rape case is iron-clad, there is no need to plea bargain the charges down. The result is that the predator is locked away where he cannot get at other children for a longer time.
What should the officer first responding to a missing child call do to secure scent evidence?
(1) Lock up, tape off, or otherwise secure the child’s bedroom and closet which contains articles with the child’s scent on them. This also secures DNA, fingerprints, and other evidence which may be helpful in locating or identifying the child. The child’s computer may help detectives discover who the child went to meet. .
(2) Make sure no one handles the child’s stuffed animals or washes the child’s bedclothes or puts them in a hamper with the clothes of other family members. Almost any kind of clothing--shoes, hat, or coat--can be a scent article to start the bloodhound on the child’s trail.
(3) Tape off the last place the child was known to be as a potential crime scene, as not only the child’s but also the predator’s scent is probably there.
(4) Protect footprints in snow, dust or mud by covering them with a clean box or plate and not walking over them, as scent rafts from the perpetrator should be in or around his footprints.
(5) If there is a visible scuff mark on a window sill or a torn screen through which the abductor probably entered the home, do not let anyone near where scent rafts may have fallen, as, for example, on the window sill and the area under the window.
(6) If you cannot wait for the crime scene technician or the bloodhound handler to collect a potential scent article, use a coat hanger to pick up the article and place it in a clean paper bag or clear evidence bag and seal it up.
What can the officers first on the scene do to protect the trailing dog’s nose?
(1) Turn off the squad car and other vehicles at the crime scene, as the carbon monoxide given off by vehicles left running can desensitize the dog’s nose. While the bloodhound handler can take the dog away from the area and let its nose “rest,” and, then, try again to pick up the scent after the carbon monoxide has dissipated, precious time is lost.
(2) Do not use flares if you can avoid it, because sulfur and phosphorus are given off.
(3) Ask nearby groves and nurseries not to spray or put out additional fertilizers until the bloodhound has completed trailing.
When should scent evidence be collected?
According to Bill Tolhurst in Manhunters , on page ix, “The very first piece of evidence to collect must be the ‘scent material.’ After that, the crime scene can be treated in the usual manner, and none of the other evidence normally collected has been damaged.” Then, when you start your dog on the scent article, the dog should be able to pick up the scent trail without disturbing the crime scene by nosing around the perimeter of the preserved crime scene for the scent trail leading away from the crime scene. The opportunity to take the predator’s scent off rocks piled over a child’s body or off the cord tying a young woman’s body to a tree was forever lost, because officers removed the rocks and cut the cord before a gauze scent pad was made.
What should the crime scene specialist do to insure scent is properly collected and preserved?
(1) Secure and separately bag more than one piece of material containing the missing child’s scent, in case one scent item gets contaminated or contains, for whatever reason, someone else’s scent. This can happen if the family’s dirty clothes are mixed together or another child slips into the bed of the missing child or tries on the child’s hat. Shoes are likely to be less contaminated than other articles.
(2) Wear new unpowdered latex gloves when bagging the scent item. Use unused, plastic, zip-lock food storage bags or clean paper bags. Properly label and store the bag for future use, preferably in a refrigerator.
(3) For items you cannot take away from the scene, create a scent-pad. For example, to get the predator’s scent if he opened the door and came into the home, place a sterile gauze pad over the door knob. If entry or exist was through the window, wipe the pad over the window sill. If the child was in the car seat when the car was stolen, wipe the pad over the driver’s seat or the car seat lock or other places the person may have touched in removing the child. If the predator’s scent is there, the gauze will absorb it. The longer the pad remains in contact with where the scent is the better: so, leave it there five minutes if possible. It is critical to keep everyone else from touching the surface until your scent articles are made. Don’t forget you can use as a scent article anything a predator eliminated at the crime scene--his blood, urine, semen, saliva, feces-- as all body fluids of an individual give off the unique scent of that person.
(4) Collect as potential scent articles anything along the scent trail which might belong to the predator. To preserve the predator’s scent on such items as dropped clothing, cigarette butts, match books, or styrofoam cups, pick up each with a coat hanger or clean stick and place it in a clean paper or plastic bag and close and seal it. Or, you can simply pick the item up by pushing the bottom of the bag out, grasping the scent material, and pulling it back into the bag, as you would pick up a dog turd. Do not use a garbage bag unless you know it has not been chemically treated as some are. If the bloodhound is trailing the predator’s scent from the scene, the dog can identify later which of these bagged articles belonged to the predator. Then, if the article has fingerprints or DNA on it, you are a long way toward proving who was at the crime scene and who fled from the scene.
(5) If you are lucky enough to have a recent model of Bill Tolhurst’s scent machine, you can vacuum the scent from any object onto the sterile gauze pad in the machine, without disturbing fingerprints and other trace evidence, as the devise has a 10-foot extension, which allows you to scoop up scent without stepping into the crime scene. In fact, Tolhurst, in his new book The Invisible Witness Scent (2000), says that his machine can take scent off of the tape used to lift fingerprints and that his machine actually enhances scent as it takes all the scent off the scent article and condenses it onto the smaller gauze pad inside the machine.
(6) Naturally, the same chain of evidence must be observed with scent evidence as with all other trace evidence.
(7) If one or more officers have touched the only scent article you know you have, say the driver’s seat of the car, have all the officers who entered or leaned into the car stand by the car when the dog is scented on the driver’s seat. It will be obvious to the dog, especially if you have practiced this scenario of the missing person, that you want him to follow the scent of the person who is not standing right there.
How can you keep scent evidence uncontaminated by different bloodhounds taking scent from it?
Bill Tolhurst shows you a picture of a scent pump and tells you how to construct and use one, on pages 228 of Manhunters (1984) and 36-37 of The Police Textbook for Dog Handlers (1991). Mr. Wood, former president of the National Police Bloodhound Association, says that you can simply let different dogs take the scent from different scent pads, provided you have made multiple gauze scent pads from the solitary scent article.
Why is retaining scent evidence important?
(1) After your bloodhound takes scent, make sure someone seals the scent material in an evidence bag, without handling it. It must be properly labeled. All the rules to establish the chain of custody must be observed if the scent article will be used for another search or a line-up identification, especially an identification in the court room.
(2) If someone reports seeing the missing child, re-scent your bloodhound on the scent material to see if the dog can trail the child from where the child was allegedly sighted. This is a quick way to confirm whether it was a real sighting. If the bloodhound finds the child’s scent there, the child was there. If not, then, it was probably not the child, just a kid who looked like the child.
(3) If the bloodhound scented on the rapist’s scent collected from one rape kit finds the culprit’s scent in another rape case, the same man may have committed both rapes. If you place suspects in a lineup, you can have the dog take scent from a scent article from either crime scene, and the dog will nose up to the person giving off the same scent.
Is there a way to freshen up scent material which has been sealed for weeks or months?
According to Tolhurst, if the scent material has been sealed up, it can keep as long as a year for identification and other purposes. If you put the bag in the freezer for 15 minutes, and then let it stand for awhile at room temperature, the moisture will activate the scent and make it easier for the bloodhound to take scent from the material.
What must be established to make your dog’s trailing find, location of evidence, or identification of a suspect admissible in court through your testimony at trial?
(1) In People v. Centolella, 305 N.Y.S. 2d 460 (Oneida County Ct. 1969), five requirements for the admissibility of bloodhound handler testimony were identified: (i) the bloodhound must be a pure breed as these dogs are known to have a keen power of scent; (ii) the dog must have been trained to trail the scent unique to any individual, that is, to scent discriminate between different humans; (iii) the dog must have proven its expertise by regularly making practice and/or actual case finds; (iv) the dog must have been started where the crime occurred or the suspect or victim was known to be subsequent to the crime; and (v) the bloodhound must have been placed on the trail within the period he has already successfully trailed in practice. If the first four conditions are met, it is unlikely that any modern court would impose the fifth requirement, as today it is better understood that a bloodhound can trail on as old a trail as he successfully trails, regardless of whether this is the first time the dog has actually been tested on that old a trail. It is, however, still a good idea to test your bloodhound on 24-hour-old trails just to be safe. The fourth requirement has been widened considerably, as the child victim can be trailed from his school bus stop where he was known to have been let out before the abduction took place. Also, drop-trailing, that is, driving the bloodhound down a long highway and having the dog check each exit to see if the child’s scent veers off there, would likely be accepted in most courts.
(2) The handler needs to give to the prosecutor a copy of the bloodhound’s trailing records detailing the dog’s experience, skill, training, and reputation. This is why it is necessary to keep trailing practice records and qualification certificates. The state attorney will enter this information into evidence to show the reliability of this particular bloodhound in staying with the scent he or she was started on and trailing until the dog finds the person or is told to stop. Terrell v. Maryland, 239 A.2d 128 (Md. App. 1968).
(3) The state attorney may have to prove the breed making the find is a bloodhound, as, in many states, only the testimony of handlers of bloodhounds has been admitted with respect to man trailing. It is probably not necessary that a bloodhound is registered with the American Kennel Club, though this registration certificate is accepted as conclusive proof the dog is a pure bloodhound, which breed is know for its keen power to scent discriminate and trail. This is not to say that the state attorney may not be able to establish that other breeds have been trained to scent discriminate and that the particular dog of another breed in question has reliably trailed on trails of a certain age in the past. It is just that in many states there is no precedent for other breeds man trailing; so admissibility is on shakier ground.
(4) Someone is going to have to testify that the article or item you took scent off of was at the crime scene or did belong to the victim. If the article has been removed from the scene, it is necessary to show that there is a proper chain of custody and that the scent evidence was properly labeled and stored until the dog was scented off it. If the defense wants the bloodhound to replicate an identification in court, it is necessary to establish that there is no reason to believe that the scent item is contaminated before the dog can be re-scented on it and troop over to nose and identify the defendant.
(5) It usually takes some corroborative evidence to support the “testimony” of a bloodhound through its handler in order to obtain a conviction. See People v. Perryman, 280 N.W. 2d 579 (Mich. App. 1979). So, other evidence at the crime scene or found along the flight path are important too, for example, fingerprints, semen for DNA comparison, shell castings, tire tracks, witness identification.
Please let me know how I can improve this scent preservation brochure! Thanks for your help.
©
THE JIMMY RYCE CENTER FOR VICTIMS OF PREDATORY ABDUCTION, INC./JRC
501(c)(3) non-profit organization since 1996
Member of Association of Missing and Exploited Children’s Organizations/AMECO
908 Coquina Lane, Vero Beach, FL 32963
772-492-0200, FAX 772-492-0210, E-mail: misujim@yahoo.com
Claudine Ryce, Executive Director and President
Member of the Florida Department of Law Enforcement/FDLE Missing Children Information Clearinghouse/MCIC Advisory Board
Member of the National Center for Missing and Exploited Children’s Team Hope
Scent Collection
