We love our dogs, don't we? Dogs are truly a gift from God. They are man's best friend, and they have been used for their highly advanced sense of smell for a variety of purposes. They can detect explosives, illegal drugs, blood, and cadavers, and they are happier than a school teacher on a snow day performing these tasks for the man or woman who offers treats and belly rubs. Believe it or not, detections dogs are even being used to detect illicit cell phones in prisons and to detect invasive species on boats at public boat ramps.
Dogs have a far keener sense of smell than humans. This is absolutely indisputable. But my dog, Tao, will attack the cat if he thinks I might back him up. You see, the cat hates Tao, and Tao holds a grudge, so he's a tattletail and feels truly justified if he can get the cat in trouble. The same rules apply to drug detection dogs.
A drug detection dog might offer a "false positive hit" if a female dog is nearby in heat or has left its scent on an article of clothing or interior carpet. This is the drug dog's way of telling his master that something interests him. It does not mean that the dog has detected drugs. The dog is not lying. In fact, he really is interested, and if he could put in for time off, he would fill out all the requisite forms and request comp time. The same might apply to any scent that the dog might find interesting: the scent of a ferret (which is unusual to the dog), scents carried by fur trappers, the smell of a new type of Yankee candle that the dog has never encountered, etc.
But dogs don't lie. They are honest to a fault. Check out this video, where a police officer provided clues to his dog in order to manufacture a false positive hit:
The above video is from Barry Cooper over at Never Get Busted, one of the nation's top drug enforcement police officers who grew disgusted with the process. He now testifies as an expert witness for the defense in these types of cases.
Unlike dogs, people lie. Check out this article by Jacob Sullum at Reason Magazine. And cops lie all the time to support a traffic stop, probable cause, or a forfeiture case. In fact, there is a term of art used in court: It's called "testilying," and it is well-document. [Read more about testilying and dropsy testimony.] It is truly an evil concept if you think about it. We are not talking about big lies but little fictions and little fibs to support a decision that is adverse to the defendant, who is clearly guilty in the minds of police and prosecutors. Courts accept these lies everday. As a matter of fact, police officers receive formal training in how to testify in court to make testimony sound more believable. They are trained to dress professionally, pause before answering a question, and to look at the jury. "Focus on individual jurors to make eye contact. Don't look down at the floor. Your credibility is being judged by the jury." Prosecutors add, almost as an afterthought, "but always tell the truth." Prosecutors don't really want to hear the truth, and police officers who testify poorly quickly retire or receive lateral transfers.
In fact, police officers are trained by prosecutors in how to make up little legal lies, and they are actively encouraged to tell these fabrications in court. "After describing what you saw, explain that you made your decision based upon a reasonable suspicion, and you then made the arrest based upon the totality of circumstances." Reasonable suspicion and totality of circumstances are legal jargon that have been rendered virtually meaningless by the fact that prosecutors repeatedly tell police officers to repeat the phrases to the point of absurdity. And it gets worse. "Did the defendant make any furtive gestures?" Who in the heck even knows what a "furtive gesture" is? Hearing this for the first time, most law students wonder if it means, "Did he give you gang sign / flip you off / act like he was going to hit you?" No, that's not what it means. But police officers testify to "furtive gestures" everyday, and it keeps people in jail.
Back to dogs, however... The fact is that police officers can give oral and visual commands for a dog to bark or react. Hand gestures and oral inflections can cause a dog to "react" because the dog wants to please his owner. And these officers live with their dogs. At the end of a shift, the drug sniffing dog goes home with the officer. Drug dogs are not like school buses, and they don't get left at the station. If a police officer wants his dog to sit, he will sit. And if the officer wants his dog to hit, he will hit. After all, just like any dog, these dogs are man's best friend, and they want treats and belly rubs. And since they can't testify, drug dogs won't reveal to jurors why they bark, sit, or otherwise react. Even if the drug dog could reveal these things, I know my dog would only betray in favor of his mommy. But before a jury, Tao would back me up.
Drug dogs are certainly a valuable asset in a variety of matters including drug detection, but the courts have focused on the reliability of drug dogs when they need to focus on the reliablity of the police officers.