cover story about police dogs, this is a very handy excuse because it is impossible to disprove, especially since there is no firm answer to the question of how long residual odors remain strong enough to be detected. In practice, an alert to residual odor is indistinguishable from a mistake. Another complication in attempting to explain fruitless car searches justified by a dog's alert is that, unless there are witnesses or a video record of the encounter, the only basis for concluding that the dog did in fact alert is that his handler claims he did. Relying on the word of an officer who may want to search a car for other reasons, based on suspicions that fall short of probable cause, poses obvious hazards. A recent search at a Border Patrol checkpoint in New Mexico illustrates both of these problems.When a vehicle search based on an alert by a drug-sniffing dog fails to discover anything illegal, police typically say the animal must have smelled traces left by contraband that was recently present. As I noted in my March Reason
Around 9:30 a.m. on February 20, Dale (who asked me not to use his last name) was driving his motorhome west on Interstate 10 near Deming, heading home to California, when he was stopped at a permanent Border Patrol checkpoint. (The Supreme Court has upheld suspicionless stops at such checkpoints, which can be as far as 100 miles from an actual border, based mainly on the need to enforce immigration laws.) A Border Patrol agent walked a German shepherd around the motorhome, the sort of inspection the Supreme Court has said law enforcement officers may conduct at will during any legal traffic stop. Dale has cameras mounted inside and outside the motorhome (as a precaution against both theft and police harassment, he says), so he has video showing most of what happened during the stop. Although the video does not show the dog during the entire circuit around the vehicle, Dale says he watched the whole thing, via the motorhome's mirrors, except for a moment when the dog was in a blind spot. He says the dog was "not making any indication to [the vehicle] by barking, scratching, or sitting and staring at any particular area." The dog's handler nevertheless signaled his colleagues with a V sign, apparently indicating that the animal had alerted. At that point Dale was instructed to pull into a secondary inspection area for a search.
Dale and his passenger parked and, following an agent's instructions, exited the motorhome. Oddly, Dale's companion says an agent told him the dog had indicated the presence of marijuana specifically, although drug-sniffing dogs generally are trained to detect several different substances, and they alert the same way to all of them. One of Dale's cameras shows that the dog entered the motorhome with its handler, wandering around for a minute or two but not showing special interest in anything. Then the handler and two other agents searched the motorhome for eight more minutes, at one point chuckling over something they picked up and at another point lifting a bed to look underneath. (Dale says they damaged the bed frame.) Although the dog supposedly alerted to the exterior of the motorhome, the agents did not search any of the compartments on the outside of the vehice. Finding nothing illegal, they sent Dale and his passenger on their way about 15 minutes after stopping them. But it turned out the Border Patrol was not through with Dale yet. A minute or so after he left the checkpoint, two agents chased him in a Border Patrol car with flashing lights and pulled him over. One of the agents had left a metal eyeglass case in the motorhome, which he retrieved, saying (according to Dale), "You do not want to be caught with this in your vehicle!" Dale found the remark (and the chase, which was not justified by anything he had done) unnerving, wondering what the hell was in that eyeglass case.
A Border Patrol spokesman, Douglas Mosier, says it was eyeglasses. "The reason for the subsequent vehicle stop," he explains, "was that the Border Patrol Agent that was assisting in the search of the vehicle inadvertently left his prescription glasses in the vehicle, and they merely sought to recover them." As for why a drug-detecting dog would alert to a vehicle that does not in fact contain drugs, Mosier gives the standard reponse: "Because of their keen sense of smell, canines are able to detect the odors long after the substance has been removed from an area." How long exactly? The question is especially relevant in this case because Dale's passenger, who has a California doctor's recommendation for medical marijuana to treat disease-related loss of appetite, says he had smoked cannabis in the motor home five days earlier. Dale's companion says one of the Border Patrol agents told him the window for detecting marijuana smoke residue is three days. Lawrence Myers, an expert on drug-sniffing dogs at Auburn University, says it is "plausible" that a dog could detect traces after five days, although "it would depend upon a lot of factors," and such a capability has never been scientifically verified.
So assuming the dog alerted, it might have been reacting to traces of marijuana smoked five days earlier. There is no way to say for sure. But how do we know the dog did in fact alert? Dale says he did not see anything that looked like a signal. When I ask Mosier what a Border Patrol dog does when it alerts, he says, "The manner in which a canine alerts varies from canine to canine." Can he describe the various kinds of alerts? No, he says, "because it is law-enforcement sensitive." I am not sure what that means, but in any criminal case involving a dog-triggered search, the handler is expected to explain how the animal signals. It's not supposed to be a secret. Myers says the Border Patrol's refusal to say what an alert looks like "makes no sense whatsoever." This caginess reinforces the suspicion that agents use dogs as props to justify searches they want to conduct for other reasons. Even in cases where a dog clearly alerts, it may be reacting to its handler's suspicions rather than the smell of drugs.
The free rein that the Supreme Court has given cops with dogs to search vehicles is disturbing enough when police use it to peruse people's cars. It is even more troubling when the vehicle is a motorhome, which contains the same sort of sensitive and potentially embarrassing items that might be found in a residence. Last month the Court ruled that police need probable cause to deploy a drug-sniffing dog at the doorstep of a home. But when the home is on wheels, a canine inspection of the exterior no longer counts as a search. It can be conducted on a whim and, depending on how the dog reacts (or is said to react), used to justify a search of this intimate space without any need for court approval.