They didn't though. Again, other facts haven't been reported. There was extensive research into the results from the dogs used to test theor success rate and I believe it was in the 60-70% range depending on dog (three were used I think). So again, not conclusive evidence at all. And the DNA found in the rental car wasn't conclusive either. It had Madeleine's DNA but not all strands that proved it could only have been from her.
However, very good lawyers will make sure that those high but non-conclusive results don't add up to a conviction. Some DAs in America, under political pressure to get a conviction, would have enough from them to nail a suspect though!