If the dog's alerts were conclusive "evidence" why did the Portuguese Prosecutors dismiss it out of hand instead of laying charges against Madeleine's parents and proceeding to trial on the strength of it?
The prosecutors saw the alerts as raising 'founded suspicions' of the McCanns which led 'inexorably' to them being made arguidos, they did not dismiss them out of hand;
Confronted with these elements, namely the possibility of the existence of a cadaver in the apartment and in the vehicle that was used by the parents, founded suspicions of their involvement were raised.
As they were summoned to depose again, while there was no plausible explanation for those situations and as they were to be confronted with the dogs' findings and with the lab information, which were susceptible of rendering them responsible as authors of crimes (at least, of neglectful homicide and of concealment of a cadaver), they were, obligatorily and inexorably, made arguidos,
http://www.mccannpjfiles.co.uk/PJ/LEGAL_SUMMARY.htm