Doesn't it seem funny that now, when a second set of DNA material is not available on objects that have already been tested, people conclude that it was never there in the first place? I can't remember another case where DNA was obtained, tested, and when a second set was not available ... it was decided that it was never there. Usually the conclusion is that all the DNA was used in the first test (that has been said in this case), or that it is too degraded for further analysis (that seems to be true in this case as well).
Can we really conclude that there was never any DNA because a second test is not possible? I think a lot of people convicted on the basis of DNA would like to have second tests performed 4+ years after the crime to see if a second test will confirm the first. If there is not enough DNA for re-testing, should all of those convicted people be released and exonnerated?
I believe it is quite common for the defense to want to do their own testing, rather than just taking the word of the lab chosen and paid by the prosecution.
And I think you can find any number of cases where it was considered problematic that prosecution testing obliterated all traces of DNA from the object in question. How courts deal with the problem varies.
ETA: Monzoo says all this better than I in his/her last post above.