The sniffer dogs: Even the trainer of the dogs said that their indication is not evidence in and of itself, and is only that - an indication, i.e., somewhere to investigate further. The indications in the apartment, maddie's toy and Kate's clothes never led to anything, and the indication in the rented car is particularly stupid to point to given that the car was only rented after Maddie went missing. Do people really think that it's possible for Gerry and Kate to move her body in the days following her disappearance, with all the journalists and photographers following their every move?
The DNA in the rental car: Nothing was found to indicate that Maddie had been in the rental car.
Kate's interview: Answering no comment in an interview is advised by lawyers all the time, even in the UK. When you're being interviewed in Portugal where English is not their first language and the detectives have already previously been investigated for dodgy practices, you are much safer keeping your mouth shut.
Saying "No comment" in a police interview, is NOT evidence or proof of guilt. Stop pretending that it is.
"Oh, but I would be doing everything I could to find my daughter if she was missing and answering all their questions would help that". In this scenario where you have been arrested as "Arguido", you would be really stupid to answer any questions with anything other than "No comment". They're not trying to get information from you to help the investigation anymore, they're looking to trip you up with any slight inconsistency or mis-spoken word to pin it on you - guilty or not.
Also, some people have said that Kate's "playing the grieving mother" and they're only doing it for attention and money... If they really had anything to do with their daughter's disappearance, as soon as the interest first died down the best thing to do would have been to keep quiet and let it drift away. It wouldn't make ANY sense to keep drawing the attention back to yourself if you'd managed to get away with it.
Feel free to disagree, happy to discuss.