The blood they found, how do they know it was madeliene's?
It's complicated and it's been a while since I had all of this information (in respect of Madeleine McCann) at the forefront of my brain

, but basically they found enough 'markers' to match the DNA found in the hire car to Madeleine's known DNA, to qualify for a solid identification as a 'match' according to UK rules. The DNA sample known to be Madeleine's came from her toothbrush and bedding at their UK home address (the police accompanied Gerry McCann to their home to collect it).
However Portugal sets it's 'match' level at a couple of 'markers' higher than we do, so the results are therefore classified as 'inconclusive' ... especially as the FSS (Uk forensic science labs who did the testing) first of all claimed a match and then mysteriously started backtracking.
There are a few really informative websites out there with a lot of information that isn't widely available from the mainstream media if anyone wants to read a bit more:
https://forum2.aimoo.com/MadeleineMcCann/category/Interpreting-DNA-Test-Results-1-940919.html
https://jillhavern.forumotion.net/forum
https://www.mccannfiles.com/
They all have links to other sites etc - including transcripts of all police interviews and translations of the book written by the Portuguese Detective - which is well worth a read.
I am - as you can probably tell LOL - of the "There's more to this than meets the eye" school of thought.
There is absolutely NO evidence, circumstantial or otherwise, that Madeleine was abducted but there are some rather odd things that point to another scenario altogether

However all of it is circumstantial and there is insufficient evidence to form a prosecution under Portuguese Law - which is why the case was shelved. Despite what the UK media would have us believe the McCanns were never 'declared innocent' or 'exonerated' by the Portuguese Attorney General - it was simply deemed that there was insufficient evidence to proceed.... make of that what you will