What the Cold Nose Knows

When it comes to something as complex as human scent, Myers believes that different dogs likely tune in to different things. And no dog is perfectly consistent. Myers's research has shown that something as mundane as dental tartar can have a ruinous effect on a dog's powers of discrimination. "Clean the teeth and you get an almost immediate recovery of smell," he says. Scent dogs also have off days, suffer allergies, get colds. "Trouble is," he says, "you can't cross-examine a dog and ask, 'Are you sure?' "




So Myers has deep misgivings about the growing number of calls he's getting to testify in rape and murder cases that hinge largely on a doggie's positive ID. "It's like the floodgates have opened," he says.




Dog scent lineups aren't new, how-ever. Estimates suggest they've played a role in more than 1,000 criminal cases in the United States, going as far back as 1923. Today, most states and the District of Columbia admit dog scent evidence as valid identification of the accused, "provided a proper foundation is laid."




Despite this long history, a scientific basis for that proper foundation has never been established. Many prosecutors try to skirt that fact by arguing that scent lineups are no more than a logical continuation of the practice of employing dogs to track fugitives or sniff out drugs—uses that have long passed legal muster. Some judges buy that argument, some don't.




The courts rely on handlers to demonstrate a dog's reliability by
submitting training records. But it's widely known in handler circles that many are loathe to record a dog's mistakes, lest the errors later be used to discredit the dog's identifications.




Research reveals that even experienced and well-trained dogs sometimes misidentify individuals. In studies conducted in Europe (where scent lineups have become tightly regulated and standardized), dogs' identification scores varied from a high of 58 percent to a low of 22 percent. Researchers have conducted such studies both on-lead (with a handler holding the dog's leash) and off, in an effort to tease out or exclude a handler's influence.




That some handlers inadvertently prompt their dogs is a major criticism of scent lineups. And the critics include some of the nation's most experienced search-dog handlers. "We have a saying in dog training circles," explains police K-9 instructor Roger Titus, vice president of the National Police Bloodhound Association. "Your body language goes down the leash." A well-trained dog becomes hyperaware of its handler's every move, Titus explains. "You lean forward, it moves. You slow down, it does too. You walk down a lineup of six baseball caps, and all you have to do is think you're at the right one, and the dog picks up on it." Some call it the Clever Hans effect, after the 19th-century equine genius whose mathematical prowess turned out to be nothing more than the horse responding to the unconscious nod of his trainer's head.




Dog-evidence enthusiasts have reason to be cautious, Titus warns. Much of the precedent-setting case law, including murder convictions, behind the acceptance of scent lineups came from the now discredited work of a single handler, who was later shown on videotape to be cuing his dog.




The expanding use of scent lineups has become a hot-button issue in the police-dog handler community. The National Police Bloodhound Association and the Law Enforcement Bloodhound Association have both developed guidelines for proper lineup procedures, while their memberships remain deeply divided over the legitimacy of the practice.




"The fact that a dog might send somebody to the electric chair places a tremendous responsibility on the handler," admits McAlhany. "That said, my confidence in my dog and myself is very high. I would feel comfortable going to court and testifying that, yes, she can use a scent article and make a positive ID."