Differences Between Tracking and Scent Lineups Are More Substantial Than Some Courts Recognize

A Texas court found that there is "little distinction between a scent lineup and a situation where a dog is required to track an individual’s scent over an area traversed by multiple persons.” Winston v. Texas, 78 S.W.3d 522 (Court of Appeals, 14th Dist., 2002). This supposed similarity, almost identity, of tracking and trailing to scent lineups, has been used by courts in applying the same foundational requirements to the admission of both types of evidence. There are, in fact, numerous differences between the two canine functions, and some are significant from a forensics perspective. The following list of differences is probably not exhaustive. Tracking and trailing descriptions are in Roman type, while scent lineup descriptions follow in italics.

1. Dogs trained to follow tracks or trails of targets usually on long, loose leads. Dogs trained in procedures designed to emphasize matching of scents correctly; dogs work either on lead or off lead in testing area.
2. Dogs may be trained in other police dog functions, or may be tracking specialists. Dogs may be trained in other police dog functions, but are generally specialists in European procedures and in the most reliable protocols.
3. Dog ideally scented to object touched by perpetrator but sometimes scented to area where perpetrator likely to have been present; dogs occasionally scented to pads. Dog scented to object likely to have scent of perpetrator or to scent pad created from object perpetrator may have touched.
4. Scent occasionally extracted and enhanced by scent transfer unit. Scent on scenting item and scents in stations of lineup frequently extracted and enhanced by scent transfer unit.
5. Dog more often following foot scent as individual human odor. Dog more often scented to objects touched by perpetrators’ hands but may be scented to item touched by another body part (e.g. elbow, face).
6. Scent source may have been touched by multiple individuals (“missing member” may be performed to eliminate non-suspects); track may have been crossed by multiple individuals. Scent source may have been touched by multiple individuals; lineup design generally precludes scents from individuals other than the suspect and foils in the lineup stations.
7. Dog must ignore cross tracks laid at different times generally by unknown individuals. Dog must choose between objects ideally scented at same time and by individuals of same gender, age, and ethnicity of suspect; objects are generally identical or alike.
8. Dog need not choose any individual but may lead to suspect. Dogs choose between a number of objects scented by target and decoys (in zero trials, no choice is correct).
9. Dogs may work in tandem or in groups. Dogs should always work alone; when trials involve using multiple dogs, equipment generally must be cleaned between each trial.
10. Object of work is to find path taken by perpetrator and find objects perpetrator may have left, and possibly find perpetrator. Object of trial is to determine if suspect was perpetrator.
11. Handler may have to know facts about perpetrator in case he encounters him or her while tracking (particularly if perpetrator may be armed and dangerous). Handler should be unaware of correct station and dog should not be able to see experimenter or other individual who knows correct station during trial.
12. Trail may be followed by more than one team at more than one time. Equipment must be cleaned between trials if dogs may have left saliva at scenting stations.
13. Trail cannot be followed after scent disappears. Test can be performed as long as scents are preserved.
14. Procedure may produce additional evidence (e.g., items dropped or abandoned by perpetrator, locations where perpetrator may have been). Procedure does not produce additional evidence.
15. Tracking occurs in diverse environments; dog may track to a building or vehicle, implicating privacy interests. Procedure generally conducted in police station or other facility.
16. Procedure rarely videotaped. Videotaping increasingly common and often required.
17. Tracking foundational requirements apply. Tracking foundational requirements require adaptation or ignoring (e.g. putting on track where perpetrator likely to have been; tracking continuously).
18. Cueing the dog generally only possible if suspect is encountered; dogs may sometimes be forced to follow a path against their inclination. Cueing the dog possible if the handler or other participant in the lineup visible to the dog knows the position of the suspect’s scent in the lineup.
19. Dog may have to be rescented if it loses trail or becomes distracted. In optimal protocols, dog will will not be rescented during trial.
20. Environment of tracking generally cannot be controlled beyond limiting interference of other investigators or bystanders. Environment should be highly controlled to avoid contamination and cueing.

I’ve discussed the distinctions between tracking and scent identification in a working paper posted on the Social Science Research Network (SSRN), Canine Tracking and Scent Identification: Factoring Science into the Threshold for Admissibility.

For a detailed discussion of the state of the law and research on scent lineups, see another working paper, Scent Identification in Criminal Investigations and Prosecutions: New Protocol Designs Improve Forensic Reliability, by Tadeusz Jezierski, Michael McCulloch, and me, also posted on SSRN.

The authors would appreciate comments on both of these papers. Please send comments on either paper to me at jensminger@msn.com.

Dog Determines Where Each Suspect Sat in Van on Night of Drive-By Murder

A 2002 California case shows how important dogs have become in the fight against violent gangs in Los Angeles. Jose Sandoval and other members of the Vineland Boys street gang drove into the territory of a rival gang and killed a member of that gang in a drive-by shooting. An officer close to the incident got into his personal car and began to call for help. He also was shot by someone in the van holding the Vineland Boys but managed to radio for help and follow the van, which soon turned into a high speed chase. Going at times almost 90 miles per hour, the van after a few minutes crashed into some parked cars and the occupants fled. A K9 unit was called and LAPD Officer Goosby arrived with Thunder. Residents of the apartment building in the area informed the officers that some men were hiding in the laundry room in the basement. Goosby took Thunder to the laundry room. The door was partially closed. Goosby issued a warning and one suspect came out, but said there was no one else in the room. Goosby let Thunder loose and Thunder alerted as soon as he went past the door. Goosby called Thunder out, then issued another warning. A second suspect came out and surrendered. Officer Goosby then took Thunder to a nearby area where another suspect was found hiding under bags of peat moss.

Thunder was the first dog on the case. Tinkerbelle was the second.

Gloves, clothing, and weapons that had been discarded by the suspects after they left the car were brought to the police station. An LAPD volunteer named Dennis Slavin had been summoned with his bloodhound Tinkerbelle. Slavin told the officers that Tinkerbelle could determine where each suspect sat in the van. This is the court’s description of how this was done:

"Slavin used a “scent transfer unit” to take a scent sample from each of the five seats in the van (two in the front, two in the middle, and a rear bench seat). The scent transfer unit looks like a Dustbuster, modified with a small frame at the end to secure a piece of gauze over its intake opening. Slavin attached a piece of sterile gauze to the unit, activated the unit, and held it against one seat of the van, pulling air from the seat through the gauze pad. Having scented the gauze with the scent on the seat, Slavin secured the pad in a plastic bag, cleaned the unit, and began again with a new pad on the next seat. Slavin then presented each of the gauze pads individually to Tinkerbelle, outside the door to the police station where defendant and his companions were held. Tinkerbelle picked up each trail at the police station entrance, and followed it to a cell. Tinkerbelle trailed the front passenger seat to Corral's cell, the seat behind the driver to Moreno's cell, and both the seat behind the front passenger and the rear bench seat to defendant's cell. Tinkerbelle trailed the driver seat to Quintanilla's cell."

There was other evidence against the defendants, and all the exceptions to the introduction of the evidence, both canine and otherwise, were overruled in the appeal. The convictions stood. People v. Sandoval, 2002 WL 519848 (Cal. App.2d Dist. 2002).

Older Bloodhounds Track Two-Day Old Trail Almost Perfectly in Multiple Environments

A professor and a member of the San Bernardino police department determined to test the tracking abilities of bloodhounds that had received more than 18 months of training against bloodhounds that had received less training. They obtained four dogs in each category and performed the following test. Subjects down trails from a half mile to a mile and a half long in five separate areas at five separate times. Two of the areas were in regional parks, a third area was a college campus, and two of the areas were in downtown San Bernardino. The subjects laid down the trails 48 hours before each dog was brought to the starting point of a separate trail. The subjects were given maps which showed them where to begin and where to end. With each subject was a partner whose scent would not be given to the dog. About 50 feet from the end point of a trail, the subject and the partner would separate and find a place to hide behind an object, such as a tree or a building. After standing in this location for about ten minutes, the subjects and the partners were driven away by a car which did not cross the trail they had laid at any point. Two days later, when the dogs were brought to the beginning point of each trail, the subject and the partner were brought back to hide in the locations where they had previously stood for ten minutes. Neither the handlers nor the researchers watching the dogs work knew where the trails went or which subjects the dogs were supposed to alert to. Scent had been taken from each subject using a scent transfer unit (STU-100, see picture), which put the subject’s scent on a gauze pad. The dog was allowed to smell the gauze pad (with no other contact with the subject) at the beginning of the trail, then commanded to TRAIL. Most of the trails had been crossed by hundreds if not thousands of people between the time the trails were laid and when the dogs began to track. At one regional park, a trout fishing contest meant more than 1,000 people had crossed the trails. The trails on the campus and in downtown San Bernardino involved tracking on cement and asphalt. Rain had fallen before the first trails were laid. Of the 20 trails that the younger, less experienced dogs followed, 12 were run to completion, with the subject found by the dog. One dog identified a partner rather than a subject in one trial. Of the 20 trails followed by the veteran dogs, however, 19 were run to completion with the subject alerted to. The researchers noted the following concerning the single veteran dog failure. “The one veteran bloodhound that did not make the find was distracted by a foul smelling dumpsite that was located about 300 yd off the trail. The handler was not able to keep the dog’s attention on the trail and decided to stop his dog. Once the dog was walked a substantial distance from the dumpsite, she continued the trail and made the find.” The researchers suspected that the poorer performance of the younger dogs was in part due to their less mature neurological systems. The two youngest dogs in the experiment were only 10 and 11 months old, respectively. Within three months of the test, both had improved to a level of 100% on subsequent tests. Lisa M. Harvey and Jeffrey S. Harvey, “Reliability of Bloodhounds in Criminal Investigations,” 48(4) Journal of Forensic Science 811-816 (July 2003).