Earlier in this thread it was said that the investigators testified that all correct procedures were followed. In the article by Thompson I cited, he discussed how Houston DNA analysts made a similar claim, even though it was false. Therefore, the testimony of the investigators in this case cannot be taken as an absolute assurance that correct procedures were indeed followed. Readers will find other items in both articles that are directly related to the case, as well being better informed about contamination in general.
Yes: if everybody is telling lies there is no case to answer. And of course everybody could be telling lies, including two independent experts at least one of whom was present for the testing. In fact everybody could be telling lies in every case everywhere: I think we should release all prisoners immediately