So why isn't it admissable in court? Why did they signal a positive result , what else could it have been that they smelled?
Some interesting comments on Reddit from a couple of years back, from someone claiming to be a cadaver dog handler:
'I am a cadaver dog handler and I think there's a very high chance of false positives in this case. The first thing to consider is that there were two dogs, but there was only one handler, and most false alerts are handler error.
As others have noted, there were huge breaches of search protocol in the vehicle search. Any dog will eventually give a false alert if you keep telling it to work the same area over and over, which is what happened. It's been awhile since I read it, but I recall that the pattern of alerts in the apartment also made me suspicious that they were reworking the dogs over the same areas over and over again in there. So they were basically asking for a false alert.
Even if the alerts were correct, though, we're talking about hotel rooms/vehicles where who knows what could have occurred. Someone crashes their bike and bleeds all over their clothes, then drops them in the trunk of the car and the fluid soaks into the fibers of the upholstery (or behind the sofa, or anywhere else the dogs alerted)? That could be enough to get a cadaver dog alert even though it has no relevance to the McCann case.
Dogs are pretty amazing and I have a tremendous amount of faith in mine, and all of their alerts have been backed up by forensic evidence. I'd still never convict someone just based on the evidence they provide, especially since on a few occasions that forensic evidence showed that, while the alert was correct (there was actually blood there), it had nothing to do with the actual mission we were on.'
They later added:
'I guess my answer to that would be that dogs are always right until they're not. This was a pretty unusual case with a lot of media scrutiny and pressure on the handler to find something, and I do think that played a role. If you watch the video another commenter posted, it's not even slight changes. I will admit I hadn't even actually watched it until yesterday (just relied on written reports), and it was actually worse than what I was picturing. The handler moved on quickly from all of the control vehicles when his dog didn't show interest, but called him back like 4-5 times to the McCanns' vehicle, tapped it, gestured towards it, etc. even after the dog had repeatedly moved on. I think even my younger dog, who has a notorious, "fuck you, I know my job" attitude so it's hard to get in her way, would give a false alert if I did that.'
https://www.reddit.com/r/UnresolvedMysteries/comments/6qq47l/questions_about_madeleine_mccann_case/