I think forensic crime labs should not be all that cozy with the police or the prosecutor's office or anyone, they should be autonomous. They should be in the business of science and fact. Being chummy with the police gives me the impression of impropriety.
For all its advances, forensic science has a complex set of problems that are only beginning to be understood and addressed:
(1) poorly run labs that do not perform and document their work through accepted scientific procedures;
(2) a relative lack of quality accreditation bodies and standards for labs and technicians;
(3) a near absence of scientific studies for some key forensic tools like fingerprints;
(4) inadequate funding;
(5) a near lack of effective independent auditing of lab performance and reliability;
(6) poor understanding and advocacy by prosecutors and defense attorneys as to lab evidence.
Making crime labs independent entities would do little to address these issues and might make them worse. Independent labs would tend to be bureaucratic stepchildren as to funding, and they would likely become the equivalent of the post office, where everyone waits on the same line with no distinctions as to the relative importance the business at hand.
Moreover, making labs independent might give them unwarranted credibility even when their results are weak. Prosecutors could say, in effect, “This is independently obtained and analyzed evidence and is not simply what the prosecution is saying. We should believe these lab results in spite of the defense attacks on these fine and disinterested scientists.”
On the whole, we are better off keeping to the principle that the police and prosecution are responsible for gathering and analyzing evidence and presenting it in court, with the defense then able to challenge it. The advocacy system is imperfect but it works.