The basic science behind DNA testing is sound enough. Each individual has DNA that varies as much as one person varies from another. With the right technology, we should be able to compare a DNA sample found at a crime scene with one taken from a suspect.
That is, we should be able to do a fair comparison of those samples as long as:
- The evidence was gathered and preserved correctly
- There was no break in the chain of evidence
- The test used to compare the samples is scientifically valid
- The test was performed correctly, and
- The testimony about the test results is not exaggerated
We already know that a mistake at any point in DNA collection and testing could destroy the validity of the evidence. But do we even know that the specific test being used is valid and produces reliable evidence?
Forensic is only admissible in court if, among other considerations, its reliability is widely accepted by the relevant scientific community. This is because, in part, jurors aren't in a position to weigh the validity of scientific evidence. More important, however, the Constitution guarantees criminal defendants the right to fully confront the evidence and witnesses against them. Defense attorneys can't do that effectively unless they fully understand the meaning of any forensic evidence and how it was obtained.
Ordinarily, defense attorneys get at such information by questioning the witness introducing the evidence about how the test works, how it was performed and the degree of certainty involved. With some recent DNA tests, however, courts have been hesitant to allow the kind of deep scrutiny that would be required for a full understanding of the test.
Why? The tests involve trade secrets, and many courts have put the protection of those trade secrets ahead of the constitutional right to confront evidence.
Basically, courts have allowed these companies to say, "trust us; these tests are scientifically valid and produce reliable evidence." Defense attorneys have been denied access to the devices' underlying data that supports their proper operation and accuracy.
There may be a break in this trend, however. A California trial judge ruled last October that the defense has the right to see inside one DNA test called STRmix. The judge ordered the state to turn over the program's source code, user manual, internal validation studies and other information over the objections of the company. The state has appealed the order and the ACLU and other public-interest groups have filed friend of the court briefs in support of the ruling.
This issue is being considered across the U.S., and all eyes will be on California's court of appeal.
Trade secrets have long been involved in much civil litigation. The company's interests are often accommodated by protective orders -- specific orders from the court that limit or prohibit revealing the information beyond the parties involved in the litigation. The issue of trade secrets is only recently becoming a concern in criminal cases, where it clashes with a defendant's constitutional rights. Reasonable protective orders in criminal cases can be fashioned to satisfy a company's concerns. But in no event should trade secrets ever trump a defendant's constitutional rights.