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Scent Lineups

By Guy J. Hargreaves

Special Agent Hargreaves serves in the Office of International Training, Drug Enforcement Administration, Quantico, Virginia.

In Colorado, a bloodhound named Yogi tracked the scent of a kidnapped 5-year-old girl for 7 hours, traveling 14 miles from the site of the abduction. While Yogi rested overnight, police officers found the girl's body only a mile from where Yogi had last followed her scent. Continuing on the trail the next day, Yogi located the suspect in a nearby apartment complex.

Yogi's resume is impressive: 4 kidnapping cases (2 convictions, 2 pending prosecution), 45 homicides (sending 14 murderers to prison), and 350 other cases (with only 1 acquittal). Thanks to a sense of smell several thousand times greater than a human's, Yogi and other dogs like him have been used to pursue fugitives, locate escaped convicts, find missing persons, and detect drugs and explosives.

Yet another use exists for the dog's keen sense of smell: Identifying suspects in a lineup. Yogi himself has identified at least 25 suspects in lineups and has close to a 100-percent conviction rate in the Colorado courts.

In the United States, scent identification lineups represent a relatively new evidentiary tool.1 As such, law enforcement officers wishing to use this technique should consult the local prosecutor or their department's legal advisor for advice on the legal principles surrounding this method of identification. In Holland, however, the Dutch National Police have conducted extensive research and testing to develop a procedure that would withstand judicial scrutiny. The method, which uses steel pipes, is designed to limit the handler's involvement in the process and eliminate contact between the dog and the suspect. This article describes the detection dog lineup technique developed and refined by the Dutch police.2


Since 1919, members of the Dutch Police Canine Unit have trained police dog handlers throughout the world. The unit began using several forms of scent identification lineups in the 1960s and developed the one described here in 1993.3

Today, the canine unit employs 15 full-time dog handlers and 15 Belgian Malinois for scent identification lineups. These clever canines sniff out the suspect in an average of 40 percent of the 900 cases they work each year.


Several different methods exist for using detection dogs to identify suspects. Dutch police dog handlers recommend the following technique.

Step #1: Collecting Evidence From the Crime Scene

First, the criminal investigator locates evidence from the crime scene. Any object that can hold a scent qualifies, including a piece of clothing or a shotgun shell. Wearing gloves and using gauze cloth and special tools to collect the evidence ensure that nothing else leaves its scent on the object.

Next, the investigator places the evidence in a sterilized glass jar or in a heat-sealed, tamper-proof bag. Properly sealed, the evidence must be stored following appropriate chain-of-custody guidelines to ensure its integrity for later use. The Dutch police have stored scent evidence for up to 3 years, then used detection dogs to identify suspects.

Step #2: Preparing for the Lineup

To conduct a proper lineup, police officials need six, 5-inch stainless steel pipes. The pipes are boiled in water or cleaned in a pressurized steam-cleaning machine, then placed in separate glass containers, each with a different colored lid.

Next, investigators select five plainclothes detectives to participate in the lineup with the subject. Even though the dogs identify suspects by scent alone, lineup participants ideally should be the same race and sex as the suspect. All participants, including the suspect, must wash their hands with a neutral soap to eliminate any foreign odor.

Each member of the lineup stands behind a glass jar, which officers have placed on the floor of the lineup room. On command, each person opens the glass jar, retrieves the pipe it contains, holds the pipe for 5 minutes, then places the pipe back into the container. Police officers supervise the entire process.

Again using gloves and special tools, police personnel retrieve the pipes and place them on the floor of the lineup room, at least 50 centimeters (about 20 inches) apart. By rolling a die, officials determine where to place the suspect's pipe; they place the remaining five at random. Each position on the floor corresponds to a number, from 1 to 6. Police officials document this information in writing.

Before the dog and its handler enter the lineup room, the person who places the pipes on the floor leaves the room, removing the glass containers. This ensures that no one influences the dog prior to the lineup.

Step #3: Conducting the Lineup

With the lineup prepared, investigators bring in the crime scene evidence and remove it from its tamper-proof container. The dog handler and the detection dog enter the room, and the handler uses forceps to hold the evidence over the dog's nose. Then, the handler leaves, and the dog goes to work.

The dog sniffs the pipes until it finds the one whose scent matches the crime scene evidence. Depending on its training, the dog will indicate a match either by picking up the pipe in its mouth or by sitting next to the pipe and barking.

As a control for the procedure, the police sometimes include a second line of pipes. Because this line does not contain the suspect's pipe, the dog should not identify any of them. Using a control lineup ensures that the dog searches specifically for the pipe that matches the crime scene evidence and does not feel compelled to choose a pipe no matter what.

Ensuring Accurate Results

In Holland, the results from detection dog lineups are admissible in court only in conjunction with other evidence linking the suspect to the crime. Still, as with any evidence, using proper procedures ensures the accuracy of the findings, and in turn, their admissibility in court. These procedures include handling evidence correctly, documenting the lineup process, and limiting the dog handler's involvement in the proceedings. Finally, the Dutch police allow the defendant's attorney to witness the lineup if requested and often videotape the dog's scent identification.

Moreover, the Dutch police certify every dog for scent identification lineups following a canine curriculum that includes 1 year of intensive training and a series of tests verifying the dog's ability to sniff out suspects. As important, although law enforcement agencies can train the same breed of dog for different specialities, such as drugs and explosives detection or tracking and scent identification lineups, individual dogs never should be cross-trained for more than one specific duty. For example, a drug dog never should conduct scent lineups because it might respond to the scent of drugs instead of linking the crime scene evidence to the suspect.


Perpetrators of rapes, murders, kidnappings, and other violent crimes frequently leave forensic evidence at crime scenes. Even with high-tech equipment at their disposal, investigators cannot solve every crime; after all, they are only human. But, by using a detection dog lineup, police investigators can collar these violent criminals. Whether tenaciously tracking a lost child or putting the paw on a criminal, canines continue to prove that they can be law enforcement's best friends.


1 See Ramos v. State 496 So.2d 121 (Fla. 1986); United States v. McNiece, 558 F. Supp. 612 (E.D.N.Y. 1983); and State v. Roscoe, 700 P.2d 1312 (Ariz. 1984), cert. denied, 417 U.S. 1094.

2 In June 1994, the author visited the Dutch Police Canine Unit's training school in Holland, where he witnessed the talents of these canines and gathered information for this article.

3 Canine units in Belgium, Hungary, and Germany also have conducted research using the detection dog lineup technique developed by the Dutch police.

Note: More advanced information on this subject during sessions instructed at the International Police K9 Conferences held annually in various locations throughout North America.


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