The very fact that the best dogs in the world found nothing to confirm Maddie's death supports the fact that she may still be alive.
Unless there are human remains around these dogs can't find anything to confirm a death. What they do is alert to the scent they are trained to find. The EVRD dog alerted in apartment G5A in two places; in the parent's bedroom near the wardrobe and in the living room behind the couch.
The CSI dog also alerted behind the couch, which suggests that both dogs were alerting to blood in that location. As the CSI dog didn't alert in the bedroom that could have been an indication that the EVRD dog alerted because a body had been there. As no body was found, the alert by the EVRD dog was simply a clue, or an 'indication' as Grimes refers to it.
So the dogs didn't find nothing, they indicated two possibilities. Forensic analysis found DNA on the swabs taken from behind the couch, but not enough to say who it belonged to. Nevertheless, something was found belonging to someone.
Both dogs alerted to the McCann's car, in particular to the key, and DNA consistent with that of Gerry McCann was found on the key. The CSI dog alerted in the boot of the car and DNA was recovered, but was not matched to any one person.
http://www.mccannpjfiles.co.uk/PJ/MARTIN_GRIMES.htmhttp://www.mccannpjfiles.co.uk/PJ/JOHN_LOWE.htm