12/19/2014 08:41 pm ET Updated Feb 18, 2015

Forensic Science Is Not CSI , in Ferguson or Anywhere Else

The other day, I wrote about how unreliable eyewitness testimony is, despite the fact that the criminal justice system treats it as solid evidence. However, this is not the only type of evidence that is far less reliable than we perceive it: There are also major shortcomings to almost all forms of "scientific" evidence used in court cases, namely forensic evidence and expert witnesses. Yet the public has been conditioned, thanks in no small part to CSI and other crime shows, to think that forensic science is perfect.

Forensic evidence is important for criminal investigations and subsequent convictions. Americans are fortunate enough not to live in a police state, so there will not always be a cop or a camera around when every crime transpires. However, the depiction on television of forensic experts doing 100% accurate science is about as realistic as their delivering snappy one-liners. Scientific methods have the potential for error, both flawed science and human error (or humans just plain lying). Nevertheless, as in the case of eyewitness testimony, juries are not informed of the shortcomings.

Most folks would be quite surprised to learn just how misguided our trust in forensic evidence is. A 2009 report from the National Research Council went into exhaustive detail on the substantial unreliability of forensic science. Essentially, DNA analysis is the only one for which there is rigorous proof that it can reliably link individuals to evidence. In general, the accuracy rates are unknown for most other forensic science practices. That's right: fingerprints, hair analysis, fiber analysis, bullet matching, teeth matching, and other practices are not slam dunk evidence. There is not even sufficient evidence that each person's fingerprints really are unique. Nevertheless, we continue to put faith in forensic evidence as irreproachable. And the lack of standard protocols across so many different police jurisdictions make it even harder to determine accuracy.

Sometimes the science leading to a conviction is later debunked, but that still may not be enough to sway the criminal justice system. This is what happened to Cameron Todd Willingham, who was convicted of murder in Texas when his three daughters died in a house fire. The accepted science at the time of his conviction concluded that it was arson and Willingham was sentenced to death. By the time of his execution date 12 years later, advances in science soundly discredited the earlier "proof" that it was arson, which was even acknowledged by one of the experts in the original investigation. However, Rick Perry was unmoved and granted no stay of execution, resulting in Willingham being executed by lethal injection. A postmortem analysis of the investigation concluded that its methodology was "hardly consistent with a scientific mindset" and "more characteristic of mystics or psychics."

Of course, this all assumes that you actually do the forensic science, which doesn't always happen. There are cases like Annie Dookhan, a Massachusetts drug analyst who lied about her credentials and fabricated test results in order to "boost her work performance"; or NYPD lab technician Mariem Megalla, who faked test results because it was less work for her, including not having to walk to another part of the building to do more paperwork.

Moreover, so-called "expert" witnesses and their testimony are not always accurate. The reality is that one can become a certified "forensic consultant" by paying $500 for a 90-minute online course. For an extra $50, they will send you a white lab coat to help cultivate the illusion that you have expertise. Or a court may allow expert testimony based on nothing at all, as happened to Lloyd Ingram, whose conviction for cocaine possession was bumped up to intention to sell because a detective said that was the case based on his "professional opinion," without a shred of explanation. On the other extreme, a court may discredit an expert witness based on subjectivities, as was the case in a New York City civil suit where a judge lambasted an expert witness and barred her from testifying further because she sighed.

The point of all this is that there needs to be healthy skepticism for forensic evidence, in the Michael Brown case and all others. Take for example the faith shown by a Darren Wilson defender in this Washington Post op-ed that boasts how the physical evidence corroborates Darren Wilson's account. (The same writer came up in my last column for his doctrinaire faith in eyewitness testimony.)

This Wilson defender cited the evidence from gunshot residue on Brown: The medical examiner concluded soot in one of Brown's gunshot wounds is consistent with that caused by gunshots from a close range, confirming that Brown was not shot while running away. However, analyzing gunshot residue is now considered highly suspect as evidence, in large part because of how much contamination can occur from contact with other things during the investigative process. For example, a suspect in a shooting might have residue on his hands not from firing a gun, but from residue on handcuffs or an officer's hands when taking him in. Of course, there's also the fact that the medical examiner found no soot in six other entry wounds.

Another defense of Wilson is that Brown's bullet wounds are indicative of trajectories that support Wilson's account. Nevertheless, analyses of gunshot wounds are also highly subjective. There are some things that can pretty much be conclusively determined, such as exit and entrance wounds, but the National Research Council report concluded "some experts extrapolate far beyond what can be supported." This includes extrapolating the directions in which bullets hit, which is not conclusive because damage made by a bullet will not be perfectly linear. However, the autopsy report for Brown includes matter-of-fact determinations of the directions in which bullets entered his body, with no mention of any shortcomings to this science.

On the other hand, it is true that fuzzy forensic science was also associated with the Brown family. Here we saw an example of a self-proclaimed forensic expert, namely Shawn Parcells, who was an assistant for the Brown family's autopsy and made many television appearances, but whose credentials did not hold up to media scrutiny. Nevertheless, despite the media hyping his involvement, there is scant evidence that Parcells was making determinations in the autopsy: The actual autopsist for the Brown family was the highly regarded pathologist Michael Baden, who in his grand jury testimony described the role of assistant as being "to help move the body and things like that," often done by a funeral director.

None of this is to say that we need to toss all the evidence out and start at square one. Nor am I saying that the evidence supporting Wilson's account is totally false. My point is that everyone -- investigators, jurors, prosecutors, journalists, and the general public -- must realize that forensic science is not absolute like on television. And as such, findings need to be treated this way when folks at different steps of the criminal justice system are making determinations.

Of course, this also means we must take steps to improve our use of forensic evidence. This includes informing jurors of shortcomings; developing standardized protocols for analyses and accreditation; further research into the reliability and margin of error for different practices, and how to improve accuracy; proper oversight of technicians, including holding lying technicians accountable; and stopping the news media from reporting as fact what the evidence merely suggests. (Good luck with the last one.)

Nothing is going to bring Michael Brown back. And it does not seem that any breakthroughs in forensic science will soon show up that will make anything more or less conclusive. However, the tragic events in Ferguson can serve as a reminder that we must not overstate the precision of evidence from forensic science, as some have been doing, because we are not living in a cop drama.