I've heard this mentioned a few years ago in a TV report on dogs used in labs that test evidence for criminal trials. Their procedure was to let the dog alone i

I've heard this mentioned a few years ago in a TV report on dogs used in labs that test evidence for criminal trials. Their procedure was to let the dog alone into a special scent-free room that contained the sample being tested, plus a few control ones. The samples were placed into containers that only let the smell out (no visual cues, even though the samples were identical-looking cotton swabs). Also, I vaguely remember a high-profile case where the evidence was dismissed precisely because the procedures for gathering and testing the samples were not followed.