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How Reliable is Forensic Evidence?

DNA analysis. Fingerprinting. Hair and fiber matching. Firearms ballistics tests. Police and prosecutors have these and other forensic investigatory tools at their disposal to help them investigate crime and prove guilt in a court of law. But how accurate are these tools? Perhaps not as accurate as you may think.

The Standard for Scientific Evidence

Whether a forensic testing method produces results reliable enough to be useful to police in investigating crimes is one thing. Whether that same method provides results reliable enough to stand up as evidence in court is another thing entirely. To be admissible in court, scientific evidence must meet the so-called Daubert standard, which requires that the evidence be based on reasoning or methodology that is scientifically valid and properly applied to the relevant facts. To determine whether a methodology is scientifically valid, a court considers the following five factors:

  1. whether the technique can be and has been tested;
  2. whether it has been subject to peer review and publication;
  3. the technique’s known or potential error rate;
  4. whether standards controlling its operation exist; and
  5. whether the technique is generally well-accepted within the relevant scientific community.

Not long ago, PBS’s Frontline took a look at a 2009 National Academy of Sciences (NAS) study that examined which of a variety of forensic methods withstand scientific scrutiny. In a story titled “Forensic Tools: What’s Reliable and What’s not so Scientific,” Frontline broke down the NAS’s report, “Strengthening Forensic Science in the United States: A Path Forward,” examining a variety of forensic techniques to see which the NAS concluded were scientifically reliable and which failed the test.

What Forensic Evidence Does The Nas Consider Scientifically Valid?

Frontline refers to DNA analysis as the gold standard for forensic tools. This is because, according to the NAS, DNA testing and analysis is one of the few forensic methods to have undergone rigorous scientific examination to determine whether it produced valid and reliable results before being allowed into evidence in criminal trials. In fact, DNA analysis satisfies all five of the Daubert factors discussed above. Similarly, forensic toxicology, or drug analysis, is what Frontline calls “a mature forensic discipline,” having been studied extensively before being put to use.

What Forensic Evidence Does The Nas Consider Insufficiently Scientific?

The primary problem with all the methodologies to which the NAS objects is that none of them, despite having been accepted in court as evidence, have the same scientific underpinnings that DNA and drug analysis do. These are just some examples:

  • Fingerprints – Fingerprint matching once enjoyed a reputation for infallibility, but has recently come under fire. Although fingerprint matching proceeds from the assumption that each individual’s fingerprint is unique, the NAS says there are no peer-reviewed studies (remember the Daubert factors) supporting this premise. Furthermore, some studies have shown that fingerprint examiners can fall prey to contextual bias, meaning that they may be more or less likely to conclude that two sets of prints match depending on how much they know about the case at hand.
  • Ballistics – The idea behind firearm analysis is that individual firearms produce particular unique markings on the bullets and cartridges that they discharge. Bullets fired from the same gun can thus be identified by these markings. But once again, sufficient studies have not been done to establish the premise that each firearm produces unique markings that always appear on the bullets it fires. Moreover, Frontline points out, there is no precisely defined process for conducting this analysis and no standard for what similarities constitute a match.
  • Hair matching – Here, the understanding is that the physical characteristics of an individual’s hair are unique and that hair found at a crime scene can be matched through examination. Once again, however, according to the NAS there are no scientifically-accepted statistics showing that hair is unique, or what proportion of a population is likely to share the same hair characteristics.

Consult an Orlando Criminal Defense Lawyer

If you have been arrested or charged with a crime, you need an experienced criminal defense lawyer in your corner. The lawyers of The Baez Law Firm, with offices in Orlando and Miami, have the skills and confidence to provide you with an aggressive and thorough defense. More, The Baez Law Firm provides its own forensic testing to counter the prosecution’s version of the story. Contact The Baez Law Firm for a consultation today.

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