Well, I know absolutely zilch about DNA. I thought somebody said that proved a familial relationship, but not necessarily the particular individual? I realize it might be long, but maybe you could shorten it and enlighten us?
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.