For mitochondrial DNA (that's DNA inherited strictly from the mother) there is question. For example, a hair without a root has only MtDNA, could have come from the person in question or his/her mother or syblings or even maternal grandmother. That is why the hairs found in case have to be considered in terms of length (could have been one of the brothers') or in terms of being chemically treated (could have beem Mom Brenda's).
Nuclear DNA (as in blood and tissue, etc.) is another matter altogether and is quite specific to the individual in question, or, of course, and identical twin. In a population as genetically diverse as we have here in the US, a 13 of 15 loci match is plenty enough for me.
That's the short version. Hope it suffices.
I understand that part about MDNA, but I don't understand how NDNA doesn't have to match all markers to be able to be absolutely attributed to a specific individual. To me, it's a "could have". Just like it "could have" identified any one of the others in the "genetically diverse" population group.
Sorry. But I'm not too good when it comes to understanding stuff like that. One time I tried to learn logic, but it wasn't logical.