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University programs in forensic science, criminology, and criminal justice have seen dramatic enrollment increases in recent years. This popularity explosion is often attributed to television series like CSI (and its spinoffs in Miami and New York), Law and Order, and NCIS. While surging interest in forensic science is a boon to some college programs, the cultural impact of these police procedurals is not all benign. Some lawyers and prosecutors are frustrated by the “CSI-effect” in which juries expect evidence in real trials to look more like what people see on television. How good is the science behind TV forensics? What do these series have to offer science teachers?
Several major categories of forensic science are frequently shown in TV depictions of crime scene investigation:
- Ballistics examines the marks on bullets or bullet fragments to determine what gun fired the bullet and where it came from. Tracing the trajectory of a bullet from a gun to its final location is essentially a physics problem. Once the bullet is airborne, its path will be determined by gravity, wind resistance, and any objects it hits.
- Trace evidence includes examining fibers, seeds, chemicals, or other materials from a crime scene that could indicate where a person has been. Many common items are made of fibers that constantly break off and stick to almost everything that touches them. Tiny fragments of our clothes are left behind when we sit in a chair, and fibers from the chair are likely stuck to our clothing. By examining these fragments under a microscope, the color, type, and even brand of the clothing may be determined, and can be matched with items worn by a suspect.
- Impression analysis examines fingerprints, footprints, and tire tracks, and attempts to match latent impressions (those from the crime scene) to those of a suspect or a vehicle. Tire size, brand, and wear can sometimes be determined from latent impressions.
- Forensic DNA analysis can be used to determine relationships among individuals or the presence of a suspect based on body fluids or hair left at a scene. Everyone has a unique genetic code in his or her DNA (except most monozygotic twins), and that DNA sequence can be extracted from the nuclei of our cells. Just as we leave fiber evidence behind, we can easily leave cells behind that can be collected and the DNA sequenced.
It is easy to find past episodes from the CSI franchise to watch in syndication, so I chose two to examine more closely. In the 2005 episode of CSI: Miami titled “Identity,” a young woman is found with facial puncture wounds and covered in slime that analysis shows to be a snake’s stomach acid. Apparently the snake asphyxiated and swallowed the fully grown woman, then regurgitated her and slithered off. The officers speculate it chose this victim because she was sunburned and radiating heat. While it is true a number of snakes can sense heat (including some large pythons and boa constrictors), and pythons have been known to attack humans, no credible reports exist of adults being swallowed.
Later in the episode, DNA testing is used to establish that the young man raised as the son of a diplomat is actually unrelated to him. This is certainly one of the legitimate uses of DNA testing, but the episode depicts a significantly shorter time than what is really needed to get results of any DNA test. CSI episodes can’t detail the 5–10 days required, so this episode makes it appear as if results are available in a few hours.
Next I watched an episode of the original Las Vegas-based CSI, “The Gone Dead Train,” broadcast in 2009. Several unexplained deaths are eventually traced to deliberate infection with the rabies virus harvested from Mexican free-tailed bats. While it is true bats can carry rabies, and rabies is a very serious illness, I worry this episode might contribute to unreasonable fear of bats. (A bat seen during the day, unable to fly, or appearing ill in any way is likely to be rabid and should be avoided.) Healthy bats pose no threat to humans and consume large quantities of insects every night; regulating the insect population is certainly a service to humanity.
After examining these two episodes and reading the synopses of many more online, I am troubled by the demographics of the typical CSI criminal. It appears most criminals in CSI storylines are women getting revenge for some past injury or injustice. The two shows I watched had five perpetrators, four of whom were women. This is in stark contrast to reality of those convicted of serious crimes in the United States: 93% of state and federal prisoners are men. I’m not asking that fictional crime shows become documentaries, but CSI’s writers seem to have a fairly low opinion of women.
It is probably not surprising to learn TV does not accurately represent the real work of forensic scientists, but the troubled relationship between mainstream science and forensics might be unexpected. At the direction of Congress, the National Research Council (NRC) investigated the scientific merit of a wide variety of forensic practices. Their 2009 report, calls on the forensic science community to strengthen the certification and accreditation of programs in forensic science, and to establish the scientific validity of all forensic science procedures. While DNA analysis is scientifically rigorous, and the probability of errors known, other common practices like fingerprint analysis and tool-mark comparison have never been subjected to full scientific scrutiny. Fingerprint matching is a combination of computer and human interpretation, particularly when attempting to match latent prints, and studies have found results depend on contextual information given to the examiner. The NRC report also encourages the forensic science community to begin to report levels of uncertainty in analysis, the standard practice in all other sciences.
Science teachers might consider using a forensic storyline to generate interest in a lab activity, like using paper chromatography to determine which pen was used to write a note. I would be cautious, however, about the science presented in actual episodes of these shows, as exaggeration is common. Finally, the NRC report on forensic science reminds us how important procedures and error analysis are to careful science work.
Jacob Clark Blickenstaff is Assistant Professor of Physics and Assistant Director of the Center for Science and Mathematics Education at the University of Southern Mississippi. He can be reached at email@example.com.
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