Last Updated on October 10, 2024
Crime shows like CSI, NCIS, Dexter, Law & Order, and Criminal Minds have allowed the public to explore the work of forensic science labs. The only problem? What makes for good television doesn’t reflect the realities of crime scene investigation units. Many investigation techniques seen on screen are exaggerated or outright fabricated. Unfortunately, many jurors go into court expecting what they see on TV to match the evidence presented to them. This phenomenon, known as the CSI effect, has been widely reported on since the early 2000s. The best way to eliminate the problem is to better educate the public about the realities of crime scene investigation, which is why attorney Peter M. Liss has chosen to expose some of the most commonly held myths about forensic science.
1. Forensic Science is Not Foolproof
While forensic science can help provide additional evidence of a suspect’s guilt, it simply can’t stand alone without good old-fashioned police work. For one thing, DNA and fingerprints can be left at a crime scene any time before the crime occurred. Officers have to create a timeline and collect other evidence to show a suspect may have been present at the scene when the crime occurred.
Beyond that, it is difficult for crime teams to extract perfect, uncontaminated samples. When samples are taken, they must follow a precise chain of command that needs to be perfectly documented, or else they can get lost, contaminated, or otherwise compromised.
The bottom line is that without other evidence, such as witness testimony, multiple types of forensic evidence, or an uncoerced confession, a single piece of forensic evidence is rarely enough to close a case.
2. Fingerprinting is Not an Exact Science
Fingerprinting may be one of the oldest forensic specialties, but its longevity only means it is subject to one of the longest-running myths about forensic science. While people often think fingerprinting is one of the most foolproof ways to identify a suspect, it’s unfortunately far from precise.
A major issue with fingerprints is that they typically only appear on smooth surfaces, so they cannot be taken from fabric, cement, or rough wood.
Even when ideal samples (meaning whole, not partial prints) arrive in perfect condition, comparing fingerprints is difficult even for experts in the field. While every individual does have a unique fingerprint, the patterns are so intricate, and differences are so subtle that recognizing a match takes a lot of skill. While computer technology has made matching prints easier, it is still not a perfect process.
For example, a 2006 study by the University of Southampton in England asked six top print examiners to review prints they had previously examined (unbeknownst to them). Only two of the six experts came to the same conclusions they arrived at in the first examination.
To make matters worse, up until a few years ago, fingerprints could not be dated at all, and even now, they can only be dated to show whether they were left within the past 24 hours. If a crime occurred outside this window, examiners still can’t tell if they are looking at prints from when the incident occurred or months before that.
A real-life example of problems with fingerprint analysis occurred when Brandon Mayfield, a lawyer in Portland, Oregon, was wrongly imprisoned for two weeks because his fingerprints were misidentified and wrongly connected to a Spanish train bomb in Madrid. The United States Department of Justice was forced to offer him $2 million and a public apology.
3. A DNA Sample is Not Enough to Close the Case
TV detective dramas need to find resolutions and wrap up storylines during the allotted time, but in reality, just because detectives discover someone’s DNA at the scene doesn’t mean they committed a crime. A DNA sample in a home or on someone’s clothes doesn’t even necessarily mean that an individual ever visited that home or encountered that individual. The same goes for plant DNA found on a suspect or their vehicle.
A rare issue known as DNA transference has resulted in a person’s DNA appearing at a location they have never even visited. Essentially, what happens is that a person’s DNA is shed onto another person, who then transfers it to another place. Researchers first tested the theory by asking volunteers to share a jug of juice at a table without ever touching each other or each other’s glasses. After only 20 minutes, samples were taken from the volunteer’s hands. Even though participants never touched one another, 50% of them were found to have someone else’s DNA on their hands.
And, of course, like fingerprints, even when DNA evidence shows someone was at the scene of a crime, there’s still no proof that they were there when the crime occurred.
Even more problematic is the fact that unless someone was previously arrested for a felony crime, the government doesn’t have a sample of their DNA to compare the results to. Police may ask a suspect for a sample, collect a surreptitious sample, or obtain a warrant to collect a sample, but if they don’t already have a suspect in mind and there’s no match in the federal or state databases, a DNA sample on its own won’t help solve the crime.
4. Blood Splatter Analysis is More of a Pseudoscience
While TV shows may depict blood splatter analysis to be just as valid as fingerprinting or DNA sampling, the science behind this forensic specialty is questionable at best and downright fraudulent at worst. It was started by a chemist named Herbert MacDonell, who experimented with splatters in his basement and eventually wrote books on the subject, representing himself as an expert on the science without ever having his laboratory or findings certified or peer-reviewed.
Because of his scientific background and how he presented himself, judges accepted his findings, and few appellate courts overturned cases based on his testimony —despite him offering practically no proof his results were accurate. As more and more courts accepted blood splatter analysis as a legitimate science, it set a legal precedent, making it harder and harder for defense lawyers and other attorneys to reject such claims.
MacDonell also taught courses in his invented field, certifying police officers as experts after only a 40-hour course. His students didn’t need any minimum educational background, and after teaching classes for 38 years, only five people failed to pass.
A 2009 National Academy of Sciences (NAS) report found that blood-splatter experts’ opinions were generally “more subjective than scientific.” The report also determined that a capable analyst should have an understanding of applied mathematics, significant figures, the physics of fluid transfer, and the pathology of wounds —scientific backgrounds lacking in officers who took MacDonell’s 40-hour workshops. In fact, MacDonell testified against the findings of many of his own students.
The NAS’ findings attracted the attention of the Department of Justice(DOJ), which commissioned its own study on the accuracy of the field. The DOJ determined that the hypotheses that serve as the foundation for blood splatter analysis are still largely untested and subject to the assumptions and errors of the analyst.
Nevertheless, bloodstain pattern analysis remains a common tool utilized by police departments and is accepted by courts. While defense lawyers may argue against its use in a case, the legal precedent makes this CSI myth hard to beat.
5. Forensic Scientists are Not Crime Scene Investigators
While it’s convenient for shows to show a person collecting evidence and then running it through tests in the lab, this would never happen in real life. Crime scene investigators arrive on the scene, protect evidence, photograph the scene, and collect evidence to send to the lab. Once the evidence arrives at the lab, it is up to the forensic scientist to test the samples.
Another difference between reality and TV is that each type of forensic science requires a different kind of crime scene investigator and laboratory scientist because each of these studies requires unique expertise.
6. Not Every Crime Requires These Investigative Techniques
Crime scene investigations and lab work are expensive. If these methods are unnecessary for a specific case, detectives won’t order them. These limitations explain why police don’t collect fingerprints to uncover who stole a bike and rarely send blood samples to the lab when someone confesses to a crime.
7. Lab Work Is Anything but Instant
Again, TV shows are subject to a concise schedule, while criminal investigations are only subject to the statute of limitations. Since there is no statute of limitations for many crimes requiring forensic evidence, such as murder or rape, the labs running these samples must process them in the order they are received —and there is often a significant backlog. On a good day, it can take a month or more to process the samples, but sometimes it can take labs years to get someone to test the evidence in a case.
8. Forensic Science Doesn’t Only Benefit Prosecutors
On TV, forensic scientists are only used by investigators to help uncover the guilty party. In reality, these experts can help a defense as much as the prosecution. Forensic experts can retest evidence samples to verify the results, test samples that police overlooked, or testify that a fingerprinting and handwriting analysis presented by the prosecution is inaccurate. Forensic scientists are even responsible for exonerating many convicted prisoners through the Innocence Project.
If you’ve been accused of a crime and would like to know more about how forensic evidence may be used in your case and whether you could be negatively affected by the CSI effect, please call (760) 643-4050 or (858) 486-3024 to schedule a free initial consultation with Peter M. Liss.
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