I have used the word blood because that's what the CSI dog was trained to find.
I have often wondered why the sample contained DNA from more than one person. I can understand that happening in a case of gang-rape, for example, but not quite how it happened in this case. If the CSI dog was as good as Grime said, there was at least some blood in the boot. Then what? Two other people bled or dribbled on exactly the same spot?
The other problem is that DNA analysis is seen as an exact science but it isn't. Different analysts can reach different conclusions about the same sample, particularly when it is from more than one person.
A man was convicted in a gang-rape case in the US because the experts said his DNA couldn't be excluded from a mixed sample. The same sample was later given to 17 analysts for retesting. Only one agreed with the original finding; that he couldn't be excluded. 4 said the evidence was inconclusive and 12 said he could be excluded.
https://www.newscientist.com/article/mg20727733.500-fallible-dna-evidence-can-mean-prison-or-freedom/
The 'inconclusive' conclusion reached by the FSS may have been correct, but a different conclusion could have been reached by a different analyst in my opinion.
Good article, thank you.
In this case, we have Keela's uncorroborated report and a total of 37 alleles from 3, possibly up to 5, different donors. If there had been sufficient material, they wouldn't have needed to resort to LCN.
The sample was mixed because there were too many peaks for them all to have come from just one person.
If one person, whether a family member or anyone else who'd used the car at some point in the past, had deposited a speck of blood, and assuming some of the alleles came from that, the other alleles could be the result of any kind of DNA transfer. Someone with dry skin (back of the hand or whatever) could easily shed cells while brushing against a surface.
Although in its infancy in the US at the time of the article below, the UK had been extracting DNA from even fingerprints at the time.
http://www.forensicdnacenter.com/resources/dna-fingerprint.htmlIn the rape case, they were comparing various suspects' profiles against the sample on the victim.
In the McCann case, I presume they were simply tasked with trying to determine if Madeleiene's DNA was present or not. 15 were compatible with those in her profile, but a number of the same alleles would be shared with others, even more so in a family car. The others, which did not coincide with hers, could have been those present in the other donor's profiles (family or not), but simply not in hers.
I'm trying to see what you're wondering about? Are you wondering if her missing alleles could have been subjectively discounted as "noise"? If so, I doubt it, as the "up to 5" would seem to cover a degree of uncertainty.
And Corte Real went to the FSS, so presumably the results were peer-reviewed.