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Things You Should Know But Don’t: Pitfalls of Forensic Science

Posted November 21, 2022

If you’re a fan of true crime, you’re likely familiar with many of the forensic methods police and detectives use when investigating a crime scene. Some are common, like DNA testing or fingerprinting, while others are more situational, like bite-mark comparisons or handwriting analysis. Most of the time you hear about these methods in passing, as a footnote to the investigation. We tend to believe that forensic evidence that links a suspect to a crime scene is reliable, if not entirely conclusive.  So we rarely question the science behind it.

But over time as the efficacy of some methods is tested, a few have fallen by the wayside—the polygraph, for example, is notoriously inaccurate and most people with even a passing interest in true crime know it’s inadmissible in court. And yet, they’re still mentioned when discussing criminal cases. Even knowing the rate of false negatives and positives, a failed polygraph can still put a suspect in a bad light. It can be difficult to shake preconceived notions that some types of evidence are infallible, but the first step is always to educate. If polygraphs are unreliable, you might start to ask yourself what other methods of investigation are faulty? The bad news is that there are a lot.  Once you start to dive deeper into the science (or lack thereof) behind these techniques, the reliance on some methods is revealed as terribly flawed.  And because those flaws can cause innocent people to be convicted or the guilty to go free, we need to take a close look.

One of the most common reasons a forensic method might be discounted is because it is too easy for bias to be introduced into the process. As we know, for something to be studied scientifically, the results must be consistent and repeatable. It there are too many variable factors involved, a method of investigation can quickly go from being good in theory to being bad in practice. For instance, both handwriting and body language analysis are two methods that have been criticized in recent years.

Bias and Subjectivity

Handwriting analysis is sometimes mistaken for a similar field of graphology, but the two are very different. Graphology focuses on trying to interpret the state of mind someone was in while they wrote something, while forensic handwriting analysis is done with the goal of figuring out whether a piece of writing is genuine or a forgery. It is done by an analyst who takes two pieces of writing (one with a known author and one with an unknown author) and compares them. They find the similarities and differences and use varying methods to discern whether or not the handwriting could have been done by the same person. While the field has gained a more complex, standardized training and certification process in recent years, “the most significant shortcoming of handwriting analysis as a science is the fact that it is ultimately subjective”.

Body language analysis suffers from a similar pitfall. In the context of police work, body language analysis is often used as a way to determine whether a suspect is lying or hiding something while being questioned. In June of 2020, it was leaked that police had included body language analysis in parts of their training. The event took place in 2015, but the science of body language analysis had already been scrutinized and debunked. Years of research have shown that body language and expressions are simply not universal and are often influenced by upbringing and cultural differences or by other outside factors. Things like mental and learning disorders, drugs, or even stress and exhaustion can widely change both body language and handwriting alike. It’s easy to imagine any number of factors that might affect a person’s actions day-to-day. This makes both methods highly subjective and unreliable for things like criminal cases where, often, someone’s life or liberty is at stake.

Junk or Incomplete Science

Some popular methods aren’t necessarily biased, but they still lack solid scientific evidence to back them up as reliable methods. Among them are things like bite mark comparisons, ballistic markings, microscopic hair examination, and even fingerprinting to some extent. There are a lot of reasons these methods have been deemed unreliable. For most of these methods, the main issue is that there is simply not enough science out there to support the claims. Often times, the methods have simply not undergone robust enough studies to prove their basic premise, as is the case for bite mark comparisons. Some fields are rapidly growing and showing more promising, reliable methods, like ballistic markings—which the National Institute of Justice found had a less than 1.2% error rate in one study. The National Institute of Standards and Technology also introduced a new, algorithm-based method of studying ballistics in a 2017 paper that also appeared to show a low false positive error rate.

The other big issue with these types of methods is that they often lack standardized practices in police contexts. From county to county, the procedure for matching things like fingerprints, ballistic markings, and bite marks differs widely. The Washington Post wrote, concerning hair examination, that “there is no consensus among hair examiners about how many… characteristics were needed to declare a match”. A Smithsonian article about fingerprinting asks, likewise, “how many points of similarity should two prints have before the expert analyst declares they’re the same? … Depending on what city you were tried in, the standards could vary dramatically”. This is a worrying pattern that I noticed while researching these methods.

When enjoying true crime stories, it’s always important to look at them with a critical eye. Unlike the fictional story about a serial killer that I tell in my latest book, Blood on the Bayou, mistakes made in real-life cases have severe consequences. Remember, educating yourself and others is the first step in improving our criminal justice system. If these pseudoscientific methods keep being accepted blindly by public and police alike, who knows how many lives could be destroyed?

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