The understanding of DNA was developed through decades of rigorous scientific study and testing.
Many forensic science disciplines have physical, chemical and biochemical principles at their core. This includes drug identification chemistry, forensic toxicology, and several types of trace evidence analyses, all of which rely on objective examination.
Many people consider DNA testing the paradigm for everything else in forensic science. This is because the amount of funding that has gone into DNA research has resulted in testing that consistently and with a high degree of certainty, can demonstrate a connection between evidence and a specific individual or source.
Some experts insist that DNA is an example of an analysis based on solid science, in a way that no other discipline can claim. And though our deep understanding of DNA comes from decades of rigorous scientific study and testing, such a black and white assessment is probably misplaced. The truth, as usual, is far more complicated.
There can be—and have been—for instance, many problems associated with DNA analysis, throughout laboratories, as well as in individual cases. In fact, mixed samples can often take as much interpretation and can be as difficult to decipher as some pattern evidence.
As in DNA analysis, many other forensic disciplines combine the use of analytical sciences with interpretive techniques. One example of this is fiber analysis. There are a number of ways to analyze a fiber, each with their own strengths and drawbacks.
Using sophisticated techniques and instruments, such as chromatography and advanced spectrometry, an analyst can do a better job of distinguishing a fiber’s qualities than with a microscopic examination alone. That said, these techniques are time consuming, costly and often destroy the sample.
That’s why the analyst typically examines the fiber with a microscope to determine whether or not the unknown and known samples could have come from the same source. Once again, the scientist’s experience—or lack thereof—can make a significant impact on the results. It should come as no surprise, then, that this type of analysis can be problematic, prone to false positive identification and overstatement of significance at trial. However, if microscopic analysis is initially used to screen for a potential match, and then followed up by more scientific protocols for confirmation, the risk of false positive identification is greatly lessened.
It is also important to take context into consideration. If an analyst does find a matching fiber, the next questions are: What does that mean? How prevalent is that fiber in the environment?