Once again, certain pro-guilt commentators appear to be too ignorant or too biased to understand the nuanced argument regarding the issue of splitting low-template DNA samples for testing purposes.
Here's the conundrum: if you have a tiny amount of DNA to work with, then regardless of the sensitivity of the testing equipment (and in fact, the more sensitive the equipment, the bigger the potential problem), there is always going to be background "noise" and other artifacts that produce false peaks or stutters in the results charts. This is somewhat analogous to the difference between identifying someone's voice if they are speaking loudly at a party, versus identifying the same person's voice at the same party if they are now speaking very softly: the background noise will interfere far more with the second scenario than with the first one.
One way to address this inherent problem in low-template DNA typing is to split the sample. If the split sample is tested twice, then the charts for the two tests can be compared and contrasted. If certain peaks and stutters are repeated exactly on both samples, then it's possible to say with a fair degree of confidence that these peaks/stutters derive from the sample itself, rather than from any background "noise" (which tends to be somewhat random in nature).
But of course there's an inherent paradox here: if the sample only contains a tiny amount of DNA to start with, then splitting it into two "sub-samples" is obviously undesirable (and may indeed be impossible). However, regardless of this clear paradox, there is one overarching factor which informs the entire argument on this issue (and which some pro-guilt commentators seem either unable or unwilling to understand): if the state is going to use DNA evidence to convict someone of a crime, then the DNA evidence needs to be robust, reliable and replicable. That is a fundamental tenet of not only justice, but also of the science underpinning the DNA evidence itself.
What it means in practice is this: if there is so little DNA on a sample that it cannot be split for the purposes of conducting two separate LCN tests, then that sample must - almost by definition - be deemed inadmissible for use as probative evidence in a criminal trial. That's because the unreliability of a single-test result at these low levels is simply too high for the result to be meaningful in the context of proving identity in a criminal trial.
And as a peripheral consideration, if there is so very little DNA on a given sample that it can't be split for testing, then - quite apart from the unreliability of test results - the underlying issue of transfer/contamination also becomes significant in and of itself. In other words, if there is a huge amount of someone's DNA on an item, one can not only get a very reliable test result, but one can be very confident that there was a genuine transfer between the person and the item at some point. If, on the other hand, there are only a few molecules of a person's DNA on an item, the problems of test reliability are compounded by the possibility that such a minute amount of DNA arrived on the item by secondary/tertiary transfer or by contamination.
Thank you LondonJohn for that readable and understandable explanation for us non-DNA literate readers!
............ ....