Radley Balko wrote a nice summary for Reason of studies demonstrating the routine misuse of explosive and drug-sniffing dogs by police. The problem is not that the dogs are not capable of finding drugs or explosives, but rather that their human companions are generally poor at distinguishing when the dogs are genuinely indicating drugs/explosives vs. when they’re just reflecting cues and prejudices they’re picking up from their human handlers.
For example, it is unlikely that dogs in Illinois are prejudices against Hispanics. Cops, on the other hand…
A recent Chicago Tribune survey of traffic stops by suburban police departments from 2007 to 2009, for example, found that searches turned up contraband in just 44 percent of the cases where police dogs alerted to the presence of narcotics. (An alert is a signal, such as barking or sitting, that dogs are trained to display when they detect the target scent.) In stops involving Hispanic drivers, the dogs’ success rate was just 27 percent.
Balko quotes from The Economist’s summary of a blinded study of police dogs that found such searches strongly contaminated by assumptions of the human handler,
The experimental searches took places in the rooms of a church, and each team of dog and human had five minutes allocated to each of the eight searches. Before the searches, the handlers were informed that some of the search areas might contain up to three target scents, and also that in two cases those scents would be marked by pieces of red paper.
What the handlers were not told was that two of the targets contained decoy scents, in the form of unwrapped, hidden sausages, to encourage the dogs’ interest in a false location. Moreover, none of the search areas contained the scents of either drugs or explosives. Any “detections” made by the teams thus had to be false. Recorders, who were blind to the study, noted where handlers indicated that their dogs had raised alerts.
The findings, which Dr Lit reports in Animal Cognition, reveal that of 144 searches, only 21 were clean (no alerts). All the others raised one alert or more. In total, the teams raised 225 alerts, all of them false. While the sheer number of false alerts struck Dr Lit as fascinating, it was where they took place that was of greatest interest.
Unfortunately, as Balko notes, the Supreme Court has chosen to give a sitting or barking dog the power to determine probable cause for a search,
The consequences of those mistakes are profound. As my colleague Jacob Sullum has explained, the U.S. Supreme Court says a dog sniff is not invasive enough to qualify as a “search” under the Fourth Amendment, so police do not need a warrant or probable cause to have a dog smell your luggage or your car. At the same time, however, the courts treat an alert by a drug-sniffing dog as probable cause for an actual, no-question-about-it search, the kind that involves going through your pockets, opening your luggage, looking in your trunk, and perusing your personal belongings. The problem is that a dog barking or sitting may be responding not to a smell but to his handler’s hunch about a suspect’s guilt. The reason we have a Fourth Amendment is precisely to prevent searches based on hunches.