Probably "they" refer to prosecution. And yeah, why is prosecution going with that lab/software only? One reason is probably the DNA available for more testing is not enough / one testing could been done reliable with DNA taken from crime scene. Other reason might be behind the scenes incentives, which seems is the defense strategy here
Even if you had plenty of DNA material, going with multiple labs comes with a risk that one of them comes with a "no match" result - and that is something that is supposed to be disclosed to defense as potential exculpatory evidence - and is a nice source of reasonable doubt for a jury. It's something that is terribly inconvenient for the prosecution when someone has already been charged with the crime...
> why is prosecution going with that lab/software only?
Presumably becquse that lab/software gave them the answer they were looking for.
Why pay for even more lab/software testing when you've already got what you want (especially when it's a possibility that the additional testing will contradict the first)?
