Canine Tracking and Scent Identification: Factoring Science into the Threshold for Admissibility

77 Pages Posted: 29 Aug 2010 Last revised: 27 Oct 2010

Date Written: August 26, 2010


Tracking evidence is useful in criminal investigations and prosecutions, but identification evidence obtained by a dog’s alert can be highly prejudicial. Where the identification is divorced from the tracking or trailing because the suspect has been removed from the trail and put in a vehicle or brought to a station, an identifying alert should not be admitted unless confirmed by a scent lineup. Scent lineup evidence should not be allowed unless conducted under circumstances designed to assure a high degree of forensic reliability. Where the tracking or trailing is continuous with an identifying alert at the end, it is appropriate to admit the evidence of the dog’s actions on encountering the suspect, but testimony regarding this encounter should be limited to stating that the dog’s alert only establishes that the suspect was present at the end of the trail. If the encounter is to be taken as identifying the defendant as the perpetrator, the prosecution should be required to conduct a scent lineup with protocols assuring a sufficient level of reliability.

A dog’s behavior on any given day will depend on its training, the knowledge of its handler, the dog’s willingness to work that day, the conditions under which the tracking or trailing is conducted, the ability of the police to isolate scents from the crime scene, and so on. The dog’s training and testing history, and the results of periodic examinations, should be discoverable by the defendant and made available to his experts. Where the conditions of the track, or the time since the dog has had his proficiency tested are sufficiently long, additional testing of the dog may be required by the prosecution or the defense to assure that the dog is capable of working as described following the crime.

The forensic value of dogs is enhanced by introducing the scientific aspects of their police work. The traditional tracking foundation is an adequate basis for delving into the various events that can occur while a dog is attempting to follow a perpetrator, but both prosecution and defense should recognize that many of the situations that can arise will implicate scientific issues that can help the trier of fact better understand the significance of the dog’s behavior. Defense counsel should not merely accept the testimony of police handlers, and should be prepared to obtain equally reliable testimony of experts on the crucial issues presented in the facts. Courts should not accept harmless error arguments to shield defense lawyers who inadequately investigate the results obtained by the police and introduced into evidence by the prosecution.

Keywords: scent identification, tracking, trailing, tracking dogs, scent lineups

Suggested Citation

Ensminger, John J., Canine Tracking and Scent Identification: Factoring Science into the Threshold for Admissibility (August 26, 2010). Available at SSRN: or

John J. Ensminger (Contact Author)

John J. Ensminger, Esq. ( email )

21 Oakwood Ln.
Rhinebeck, NY 12572
United States
917-613-4960 (Phone)


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