We are talking about forensic evidence and just how reliable it is. In Raleigh and every other city in the country, just a tiny piece of forensic evidence can lead to or clear criminal charges. The term “forensic evidence” carries a good deal of weight, because it implies that the evidence is based on scientific or technical analysis. This isn’t always the case, though.
DNA testing is perhaps the most reliable and certainly the most widely accepted forensic tool in use today. There is more science to DNA testing than there is to, for example, fingerprint analysis; and, there is more empirical data to back up DNA testing methods.
Still, a DNA test is not infallible. The sample could be damaged or contaminated, or the comparison data may be faulty or too small a sample. The expert describes DNA test results in terms of probability — the expert is 89 percent certain that the DNA from a cigarette is a match to the suspect’s DNA.
Less scientific are handwriting or questioned document examiners. Similar to a fingerprint analysis, the test is a comparison of a known handwriting sample to the questioned document. For the most part, this method is used to verify signatures rather than laundry lists or love letters, because a signature is more consistent over time than everyday handwriting is. One of the chief criticisms of questioned document analysis is that a person’s handwriting naturally varies from day to day or even pen to pen.
While experts consider DNA evidence to be analytical evidence, then, they consider fingerprinting and questioned document evidence and the like to be pattern or experience evidence. With pattern evidence, the science is less rigorous. The comparisons are more subjective.
In future posts, we will discuss other types of pattern evidence as well as the courts’ acceptance of forensic evidence in general.
Source: Washington Post, “How accurate is forensic analysis?” April 16, 2012