I recently saw an article which raised questions about scent line-ups conducted by police dogs. This article was brought to my attention by a friend who had some questions about the article and video that they saw, based on the fact that they encounter these line-ups in their work. Below is the video of the actual lineup that was conducted and later proven to be faulty. Later, in this article, I want to discuss how, in my opinion these line-ups can be improved to better serve law enforcement.
Many departments in the US are now utilizing scent line-ups as an investigative tool while many agencies in Europe have been using line-ups as evidence for years. In order for this method of investigation to be successful, there is definitely a foundation of training (both dogs and humans) that must take place. Dog teams should be able to clearly demonstrate a track record of accurate and effective recognition of target odor during scent line-ups in training before ever attempting to utilize this investigative tool during an actual case. I believe that this demonstration of accuracy should be recorded and properly documented over a number of months before the handler should ask the dog to perform in a real life environment.
Procedures should be established for scent line-ups in order to reduce the risk of contamination by the handler and others assisting in the investigation. In the video, you can clearly see the investigator handling the samples that are being used in the line-up. Handling these odor samples in this manner will undoubtedly contaminate them. Each dog handler that conducts scent line ups should have a documented method of performing them and should be able to demonstrate and articulate the procedures that are put in place to minimize contamination as much as possible. These line-ups should be set up similar to a scientific procedure rather than typical drug or explosives detection training.

Bloodhound
Another aspect of training and performing scent line-ups that should be considered is what should be expected of the dog in the event that they encounter the target odor. In a nutshell, the dog should demonstrate a clear and discernable alert. This indication should not be something that takes the handler fifteen or twenty minutes to explain to the layperson in order for them to understand. This indication should be clearly recognized and understood by anyone watching the line-up being performed (either live or on video).
You should also take into consideration that the target odor should not always be included in the samples presented to the dog while training and establishing procedures for line-ups. The dog should be allowed an “out” in the event that they sniff all of the samples and they determine that there is no match with the target or suspect odor. The dog should be rewarded and encouraged to be accurate, not to always find a match. This is important because there will not always be a match to your suspect sample given a particular line-up. This scenario should also be included in your training program so that the dog understands what is expected of him in the event that there is no “match”. You should also consider having some type of “negative indication” where the dog clearly demonstrates that there is no match to the sample that has been presented to him.
Consistent training and effective reinforcement is key in any type of dog training program in order for them to be productive and maintain accuracy. I believe that this is imperative when performing scent line-ups as evidence or as an investigative tool. By establishing and effective training program, doing your homework and putting some controls and procedures in place to limit contamination and the risk of a false indication, K-9 teams can be efficient and productive in performing scent line-ups to identify suspects in criminal cases.














