This dog can send you to jail: how cops and their canines manufacture probable cause.

• Author: Sullum, Jacob

ROBERT J. BURNS, a 55-year-old retired nurse who lives in St. Louis, was returning from a trip to the West Coast last October when his white Nissan pickup truck was pulled over on Interstate 40 near Amarillo. Burns was carrying a 12-foot aluminum fishing boat on top of the truck, and he had been struggling against high winds that kept pushing him toward the shoulder. The sheriff's deputy who stopped him thought he might be drunk.

"He asked me to step out and come back to his car," Burns says, "and that's when I noticed the dog in the back seat, a yellowish Lab. I explained that I hadn't been drinking and my getting on the shoulder of the road was strictly from the wind. He said that he was going to write me a warning, and I said, 'OK, that's fine.' He asked me if I had any drugs in the car. I said, 'No, sir, I don't do drugs, and I don't associate with people who dog He asked me would I mind if he searched my vehicle, and I said, 'Well, yes, I would mind if you searched my vehicle.'"

But thanks to the U.S. Supreme Court, the deputy did not have to take no for an answer. In the 2005 case Illinois v. Caballes, the Court declared that "the use of a well-trained narcotics-detection dog ... during a lawful traffic stop generally does not implicate legitimate privacy interests." So the deputy was free to walk his dog around Burns' truck. "He got out with this dog and went around the car, two or three times," Burns says. "He came back and said the dog had 'passively alerted' on my vehicle." Burns, who is familiar with drug-detecting dogs from his work as an M.P. at Edwards Air Force Base in the 1970s, was puzzled. Properly trained police dogs are supposed to indicate the presence of drugs with a clear, objectively verifiable signal, such as sitting down in front of an odor's source or scratching at it. Yet "the dog never sat down, the dog never scratched, the dog never did anything that would indicate to me that it thought there was something in there."

The deputy and another officer who arrived during the stop nevertheless went through Burns' truck for half an hour or so, reaching up into the boat, perusing his cargo, looking under the seats and the hood, examining the gas tank and the undercarriage. They found no trace of drugs, although they did come across the loaded pistol that Burns mentioned to them once it was clear they planned to search the truck.

"They were cool with the gun," Burns says. "If it had been California, God knows what would have happened." He was so relieved that he barely minded the delay and inconvenience, which stretched a brief traffic stop into more than an hour. "I'm not a lawyer, and I'm not a super-libertarian," Burns says. "Once I realized that the pistol was not going to be an issue, man, they could have spent all day going over that car and under that car. My only concern was that one of the guys might have slipped something in to cover up for the fact that they didn't find anything."

That's one way of looking at it. But even if you are neither a lawyer nor a super-libertarian, you might wonder I) how often this sort of thing happens, 2) how it came to be that police can get permission from a dog to rifle an innocent man's belongings, and 3) whether that state of affairs is consistent with the Fourth Amendment's guarantee against "unreasonable searches and seizures." The answers, in brief, are 1) fruitless searches based on dog alerts happen a lot more often than commonly believed, 2) dogs acquired this authority with the blessing of credulous courts mesmerized by their superhuman olfactory talents, and 3) this dog license is hard to square with the Fourth Amendment, unless it is reasonable to trust every officer's unsubstantiated claim about how an animal of undetermined reliability reacted to a person, a suitcase, a car, or a house.

All of these issues come together in two cases the U.S. Supreme Court heard a few weeks after Bob Burns was pulled over. Florida v. Harris raises the question of how a judge knows that a dog's alert is reliable enough to justify a search. Florida v. Jardines asks whether police need a warrant to use a drug-sniffing dog at the doorstep of a home. These cases, which will be decided by this summer, give the Supreme Court an opportunity to reconsider its heretofore unshaken faith in dogs, or at least limit the damage caused by the amazing canine ability to transform hunches into probable cause.

'A Creature of Legal Fiction'

The foundational text of the courts' canine cult is U.S. v. Place, a 1983 decision involving an airport search that found a kilogram of cocaine in a suitcase to which a dog had alerted. The Supreme Court unanimously concluded that the Drug Enforcement Administration (DEA) violated the Fourth Amendment by keeping the bag for 90 minutes before presenting it to a dog. But instead of stopping there, Justice Sandra Day O'Connor, in a majority opinion joined by five of her colleagues, gratuitously ventured into an issue that had not been addressed by the parties to the case and did not need to be resolved for the Court to decide whether the seizure and search were legal. O'Connor opined that "a 'canine sniff' by a well-trained narcotics detection dog ... discloses only the presence or absence of narcotics" and "does not expose noncontraband items that otherwise would remain hidden from public view." Because of this specificity, O'Connor concluded, "exposure of respondent's luggage, which was located in a public place, to a trained canine ... did not constitute a 'search' within the meaning of the Fourth Amendment."

Two decades later, when the Court extended this principle to cars in Caballes, dissenting Justice David Souter noted that O'Connor's conclusion "rests not only upon the limited nature of the intrusion, but on a further premise that experience has shown to be untenable, the assumption that trained sniffing dogs do not err." In reality, Souter said, "the infallible dog ... is a creature of legal fiction." Souter cited examples of dogs accepted as reliable by courts that had 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."

If anything, Souter gave drug-sniffing dogs too much credit. A 2011 Chicago Tribune analysis of data from suburban police departments found that vehicle searches justified by a dog's alert failed to turn up drugs or drug paraphernalia 56 percent of the time. In 1979 six police dogs at two public schools in Highland, Indiana, alerted to fro students, only 17 of whom possessed contraband (marijuana, drug paraphernalia, and cans of beer), meaning the false positive rate was 66 percent. Looking at the performance of an Illinois state police K-9 team during an 11-month period in 2007 and 2008, Huffington Post reporter Radley Balko found that the dog sniffed 252 vehicles and alerted 136 times, but...