You are making a hypothesis to justify your claim that positive identification is impossible. However, your hypothesis is that positive identification is impossible if there are additional DNA traces that cannot be eliminated. I'd like to propose a counter-hypothesis (actually I already have, but you haven't satisfactorily addressed it).
Suppose only ten DNA traces were found in hotel rooms and hire cars that could not be identified and eliminated, and ten names were found on hotel registers and car hire documentation. Can we therefore assign, with a reasonable degree of confidence, those ten DNA traces to those ten individuals? In order for a false positive to be recorded, we require two things to have happened:
(1) Some other individual has left DNA traces in both hotel room and hire car. You've come up with a possible explanation of that.
(2) The individual we believe we have identified has left no DNA traces in either the hotel room or the hire car. You have not come up with even a vaguely plausible explanation here. How can one of our suspects drive a hire car and occupy a hotel room without shedding any skin or hair? Gloves while driving might explain lack of skin flakes on the driving wheel, but what about debris and detritus elsewhere in the car?
Remember, we have plenty of time for a very thorough analysis of the scene; the DNA profiles weren't produced until over a year after the attacks. Until you can explain how one or more of the hijackers could have left no DNA traces whatsoever in their hotel room or hire car, then you haven't established your claim.
Dave
Your question is fair.
In summary, how could a terrorist use a hotel room and rental car without leaving a trace of DNA?
IMO finding his DNA in just one place and not both is enough to cast reasonable doubt. Thus, IMO, it would only be necessary for him to fail to leave a trace of DNA in a single location, and not both.
So, is it at all common for DNA to not be very traceable, even after a paper trail establishes recent use? Or, is DNA readily available, with a little hard work, in most cases?
First of all I think it is important to establish the following;
DNA identifications are made by comparing DNA profiles from human remains to DNA profiles from reference samples. There are several potential sources of reference samples:
1. personal items used by the victim (e.g., toothbrush, hairbrush, razor) and banked samples from the victim (e.g., banked sperm or archival biopsy tissues stored in a medical facility);
2. biological relatives of the victim (i.e., “blood kin”); and
3. human remains previously identified through other modalities or other fragmented remains already typed by DNA.
http://www.massfatality.dna.gov/Chapter2/
Notice the use of source. Interchange origin and we have the same sentence.
Thus, if we assume the above statement to be true, process of elimination is not sufficient enough to establish DNA source, or origin.
With that said, lets consider the following;
“Cellular material for use as a potential reference sample may be derived from items such as hair, stamps, envelopes, toothbrushes, and razors. However, the use of personal items for reference samples can be problematic because the quantity of DNA that can be isolated is often minimal. In addition, ensuring before testing that only the victim used the item can be difficult”.
http://www.massfatality.dna.gov/Chapter2/
So lets say a we have a terrorist who isn't loosing his hair, or perhaps has a bald head. Only stayed in the hotel a short time. In addition the cleaning lady did a good job cleaning, right after he exited the hotel.
With this in mind, and the quote I provided, I think it is reasonable to assume that a terrorist could have possibly not left a detectable DNA sample to be collected.
In summary, it is not beyond a reasonable doubt that a DNA sample couldn't have been detected in a hotel room or a rental car after terrorist use.
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