Evidence in Criminal Cases: Forensic Science or Junk Science

There is no doubt that science and technology have had a profound impact on criminal investigations and prosecution. DNA, fingerprints, hair analysis, bite mark evidence, ballistics, blood spatter, polygraphs, and more have all been instrumental in obtaining criminal convictions. For many jury, the mere mention of scientific evidence is enough to destroy reasonable doubt. Testimony from a ballistics expert or other forensic expert can be enough to clinch a conviction for the prosecution. After all, science is fact. Science is irrefutable. Scientific evidence is proof of guilt.

Except when it's not.

Remember, at one time, scientific theory held that the world was flat. In 1930, Pluto was classified as a planet -- until it was demoted in 2006. And then in 2014, it suddenly became a planet again. At one time, leeches and a good bleeding were considered the cure for almost any ailment.

So let us just go ahead and acknowledge for a moment that science and scientific theories are continually evolving. In some cases, that just might mean that the scientific evidence a jury hears is not quite the solid proof of guilt they might believe it to be.

A Popular Mechanics article entitled "CSI Myths: The Shaky Science Behind Forensics" describes the case of a man convicted of murder based on bite mark evidence, or "forensic odontology."  The only evidence connecting the man to the crime was the expert testimony that bite marks on the victim's body matched the defendant. He was sentenced to 25 years in prison. 

However, 15 years later, he obtained full records from the case, which revealed that police initially had another suspect--the man who discovered the body. He sent a letter to the man saying that he was requesting DNA testing of the evidence in the case. The other suspect committed suicide upon receiving the letter, and the subsequent DNA evidence exonerated the convicted man and indicated that the man who "discovered" the body was, in fact, the murderer.

The same article reports that since DNA testing has become available, some 200 convictions have been overturned; at least half of those convictions were based on forensic evidence. 

Why are people so quick to believe "science?" According to the article, juries associate forensic analysis with the stories they see in popular culture:

"Jurors routinely afford confident scientific experts an almost mythic infallibility because they evoke the bold characters from crime dramas. The real world of forensic science, however, is far different. America's forensic labs are overburdened, understaffed and under intense pressure from prosecutors to produce results."

This is known as the "CSI Effect."

Forensic evidence is often relatively new science that makes broad assumptions and is often based in untested theories:

"Bite marks, blood-splatter patterns, ballistics, and hair, fiber and handwriting analysis sound compelling in the courtroom, but much of the "science" behind forensic science rests on surprisingly shaky foundations. Many well-established forms of evidence are the product of highly subjective analysis by people with minimal credentials—according to the American Society of Crime Laboratory Directors, no advanced degree is required for a career in forensics. And even the most experienced and respected professionals can come to inaccurate conclusions, because the body of research behind the majority of the forensic sciences is incomplete, and the established methodologies are often inexact."

In the upcoming weeks, we will be exploring some of these forensic scientific theories, their role in the courtroom, and the concerns over using these types of evidence as proof of guilt.

Image Credit: Chad Miller