If this were the case, would someone not have challenged it in court by now? If the dogs and their handlers were challenged in a controlled trial and shown to be biased, that would make for a useful test case.
"Handlers were falsely told that two conditions contained a paper marking scent location (human influence). Two conditions contained decoy scents (food/toy) to encourage dog interest in a false location (dog influence). Conditions were (1) control; (2) paper marker; (3) decoy scent; and (4) paper marker at decoy scent. No conditions contained drug or explosive scent; any alerting response was incorrect. A repeated measures analysis of variance was used with search condition as the independent variable and number of alerts as the dependent variable. Additional nonparametric tests compared human and dog influence. There were 225 incorrect responses, with no differences in mean responses across conditions"
"To test this, we influenced handler beliefs and evaluated subsequent handler/dog team performance according to handler-identified alerts. The overwhelming number of incorrect alerts identified across conditions confirms that handler beliefs affect performance."
The FBI spent 4 decades grossly lying about their ability to analyze hair. Think about that. The charade actually went on so long that some people would have lived their entire adult life, their entire career lying their asses off. It was later found that at least 90% of cases contained errors.
During this time someone could have similarly proved that it wasn't so because were it so surely someone could have challenged it.
An alternative explanation is that forensic science or indeed any sort of science as practiced by law enforcement has always been a joke and the bar to do something about it is always very very high.
The cost of challenging anything is often prohibitively expensive both in terms of legal costs and in risk of drawing a sentence several times worse than a plea and any case which might result in police losing a valuable tool can be mooted by simply dropping that particular case after that high bar is met.
Remember also that the prosecution and the judge aren't scientists but ARE colleagues. Perceptively evidence from dogs are brought only when they actually find something so even if they don't provably always "work" in the scientific sense they perceptively help them nail bad guys. The idea that the judge would be liable to remove that useful tool because it didn't pass scientific muster is both optimistic and naive.
Police science is a parallel world of non-science. Over and over, fake science like hair id, bite mark analysis, fire, shaken baby, excited delirium, and others are debunked. But the courts have been terribly uninterested in hearing science contradict police-science.
To be clear: courts have their own way of deciding disputes, and that process has distinct differences from the scientific model. E.g. stare decisis is actively hostile to new evidence; appeals may not reference new evidence; police practices are given deference as experts in their own magisterium, and may not be held to normal scientific practice; and others.
To do that, dog should be handled by someone who is not their regular police handler. Then they would claim he doesn't know how to handle the dog properly, or doesn't have the required "soul bond" with the animal. Can't win against crooks.
> To do that, dog should be handled by someone who is not their regular police handler.
Not necessarily if the experiment is double blind. (Or tripple blind I guess because it is the dog, the handler and the on-site experimenter who are not aware of where the samples are hidden.)
