As I understand it---touch DNA is controversial because it can be transfered indirectly, meaning a person who never touched an item can still have their DNA present on it.
Defense attorneys have successfully argued against its admittance in cases such as the Daniel Holtzclaw case and the Timothy M. case.
It's not that the
testing of touch DNA is inaccurate--it's still highly accurate. The issue is that there is the chance that the DNA was deposited innocuously at a different time, which leads to false positives.
For example, if Person A shakes hands with Person B, and Person B later touches an object, Person A's DNA might be found on that object even though they never directly touched it. See (
Bruckheim & Patel).
Given that controversy, what I previously thought would be a slam dunk in this case may not be. That is, of course, if the DNA really is touch DNA and not DNA from saliva or blood. It's being reported as touch DNA but I haven't read LE or any of the attorneys confirming that.
Yes - but the possibility that the second person leaves no DNA is vanishingly small. That's why the initial report says "single source" DNA (as opposed to, say, the glove box DNA in the Morphew case - which contained partial profiles of two or more different people).
That's why the SNP's are studied - these are the places where we vary. The chances of even siblings having the same betaglobin marker + same neuregulin marker are about 25%. For those two siblings to share a third unusual (highly variable marker) such as for proline dehydrogenase is much smaller. And so on. Each time we add a locus that has 400-1000 alleles, we have the possibility of many individuals who are distinct.
It would be very unlikely for there to be blood on the sheath and not have it mentioned in the same sentences as we already have seen for the DNA. And it doesn't matter - except that if there were blood, we would expect an injury on BK, which so far, seems not to be the case.
Since the DNA was on the use point of a tool, and we know that humans use their hands and fingers to operate such items, it would highly surprising if it were not epithelial DNA. As someone who reads a lot of forensic DNA research, I'd say it almost goes without saying in the forensic community that epithelial cells are the major source of forensic DNA.
If the profile had been mixed (some other man + Kohberger) then yes, the defense could argue that he shook hands with someone at a knife shot who then immediately grabbed a sheath (that had been cleaned off for some reason) and now there would be TWO people's DNA there. Knife shop people do not usually wear gloves, IME.
My best guess is that while BK did try to clean up the knife sheath, he had used that snap many times and each time, another few layers of epithelial cells were deposited. He might even have been able to wipe off or destroy the upper layers. But, just as epithelial cells do on our bodies, they do layer nicely and protect each other - the bottom layers, pushed down by the use and reused of the snap - had enough for several DNA samples.
ALL of which belonged to BK.
I've mentioned before that we suit up in the lab and in crime scenes to avoid our own epithelial DNA from being deposited or BREATHED onto the objects.
So if we allege that some other person collected and deposited BK's DNA deep inside the snap, they had to have decided for some reason to use DNA as a foil in an elaborate crime set-up. While suited up much like an astronaut.
And what tools would they need to get the DNA from Kohberger and onto the sheath? Well, only tools that one would find in a lab. Also sterile or even more stranger DNA would be found. There's no way to know, after a handshake, just where the other person's DNA Is - on your hands (gloved hands in this case). BK himself seems way too particular and into crime scene analysis to be NOT wearing gloves - but the store clerk is? Doesn't pass Occam's razor IMO.
IMO
nij.ojp.gov
