Back in 2005, when the Supreme Court approved the use of drug-detecting dogs during routine traffic stops, dissenting Justice David Souter noted that "the infallible dog…is a creature of legal fiction." A recent investigation by the Chicago Tribune supports Souter's conclusion.
Examining records of traffic stops in the Chicago suburbs from 2007 through 2009, the Tribune found that police turned up drugs or drug paraphernalia in only 44 percent of the vehicles to which dogs "alerted." The dogs' defenders said some of the false alarms may have been due to traces of drugs that were in the cars at some point in the past. But even they conceded that was not the whole story.
Poor training of dogs and their handlers, coupled with cops' unconscious signals to the animals, seems to account for a large portion of fruitless searches. As one expert told the Tribune, "The dogs are only as good as the handlers." State Rep. Jim Durkin (R–Western Springs), a former Cook County prosecutor who wants to create certification standards for drug-detecting dogs, calls them "probable cause with four legs."
That's because the Supreme Court has said a dog sniff, although it does not qualify as a "search" within the meaning of the Fourth Amendment, can be used to justify a physical inspection that does. In the case of a traffic stop, that could mean detaining a motorist for a half-hour or more while cops pull apart his car, looking in the trunk and the glove compartment, checking under the rugs, digging into the seats, going through bags, and attempting to locate hidden compartments.
In treating a canine alert as grounds for a search, the courts assume that dogs are furry machines that virtually never malfunction, indicating the presence or absence of drugs with something like 100 percent accuracy. But Justice Souter cited examples from court cases of dogs with error rates of up to 38 percent. He added that "dogs in artificial testing situations return false positives anywhere from 12.5 to 60 percent of the time." The Chicago Tribune's analysis puts the error rate at the upper end of that range, which would mean the Supreme Court is allowing police to search people's luggage and vehicles based on a probable cause generator that is wrong most of the time.