Why don't they just redo the analysis with a few other software packages?
Business incentives presumably reward all such companies for helping the police get convictions, so it doesn't seem a far-fetched concern.
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)?