Dogs have a 20-40% success rate - they alert to false positives more often than they are correct. That's for the best dogs properly trained. They are extremely sensitive and lack the understanding to discriminate between sources. So, for example, a dog trained to detect human blood will alert to the remains of a drop of blood from when someone grazed or cut themself months earlier. Or years earlier. Corpse detection is even less reliable. For example, one of the two dogs used in the Madeleine case alerted to human remains that were dated to the 16th century. This is why dog findings are not considered evidence either in court or by the police. Maybe in CSI, but not in reality. In reality, they are considered to be a source of possible leads - if a dog alerts at a specific place, it's considered a good spot for people to investigate and possibly find evidence.
Madeleine's DNA was not found in the hire car. What actually happened was that one of the dogs alerted to the boot of the hire car, which was examined in minute detail and all that was found was weak traces of DNA from multiple people none of whom could be identified (at best - the samples from some parts of the trunk weren't even good enough for any DNA to be found). A hire car having traces of DNA from multiple unidentifiable people on it - well, what would you expect from a hire car? Of course it has traces of multiple people.
Even if Madeleine's DNA had been found in the car (
which it wasn't), DNA evidence is far less meaningful than it's made out to be on CSI et alia. It doesn't even prove that a person was somewhere. For example, if an item of clothing worn by someone (or something they held or a brush they used, etc, etc) is put somewhere then DNA evidence of that person can be found in that place. Even though they were never there.
The DNA analysis reports are publically available. You can conveniently see them yourself by clicking
http://www.mccannpjfiles.co.uk/PJ/JOHN_LOWE.htm
A photofit that looks like someone (assuming this photofit even exists - much of the stuff written about the case is just made up, like the claim that Madeleine's DNA being found in the car when it wasn't) means very little. A photofit will look like a lot of people even if it is accurate (and human memory very often isn't).
You've been misled.