NewScientist has a story about a criminal case that demonstrates how scientists can disagree about statistics regarding DNA analysis:
The DNA analyst who testified in Smith’s trial said the chances of the DNA coming from someone other than Jackson were 1 in 95,000. But both the prosecution and the analyst’s supervisor said the odds were more like 1 in 47. A later review of the evidence suggested that the chances of the second person’s DNA coming from someone other than Jackson were closer to 1 in 13, while a different statistical method said the chance of seeing this evidence if the DNA came from Jackson is only twice that of the chance of seeing it if it came from someone else…
[W]e show how, even when analysts agree that someone could be a match for a piece of DNA evidence, the statistical weight assigned to that match can vary enormously.
I recall reading something recently that suggested while the public thinks having DNA samples in a criminal case makes the case very clear, this is not necessarily the case. This article suggests is a lot more complicated and it depends on what lab and scientists are looking at the DNA samples.