20 million viewers tune in to watch each episode of CSI: Crime Scene Investigation, making it one of TV's greatest hits. Much of the allure of this high intensity crime show is the forensics, conducted in high tech labs in big cities. In CSI, and other popular "who-dunnit" crime shows, attractive actors and actresses test DNA samples to put criminals behind bars. While the process is not nearly as easy or simple as T.V. presents it to be, DNA testing is a very real part of an actual crime scene investigation. Prior to the boom in technological advances, fingerprint evidence ruled in court cases. Lawyers, judge and jury relied mainly on these unique prints to figure out who committed the falsehood and instill justice. Now, there is a new way to prove defendants guilty or not guilty, known as DNA evidence or DNA profiling in the court room.
This process first emerged in 1985, and has progressed in leaps and bounds since that time. DNA has not only convicted guilty criminals, but it has allowed many wrongly accused men and women to go free. Here's how it works: every organism has a unique thread of DNA. These chemical fingerprints can help to point to a suspect in a crime, or to incriminate a citizen. DNA is a biological molecule that appears as a long twisting chain. This is known as a double helix, and it serves as a blueprint for everything in your body. DNA is made up of four nucleotides: adenine, cytosine, guanine, and thymine. These nucleotides link up to each other, adenine matches thymine on the double helix while cytosine and guanine band together. This is the same in every human being. Only one-tenth of a single percent of DNA differs from one person to the next.
This is where chromosomes come in. Your DNA is comprised of 23 pairs of chromosomes, and in each pair one member comes from your mother while the other comes from your father. This unique combination of your mother and father's DNA makes you unique and unless you have an identical twin, you are the only one with that chromosomal makeup. These variable regions are used to generate a DNA profile using blood, hair, or any other body tissues or products that are left at the crime scene. The more sample points that line up between the DNA from the crime scene and the DNA of the suspect, the more the possibility that he or she is guilty of the crime.
DNA evidence can be anywhere, which is part of the reason that authorities take extreme caution on crime scenes. Whether it's hair, saliva, blood, skin, sweat, or any other body fluids, they can be used to identify the criminal. Oftentimes crime scene investigators look for weapons, hats, masks, facial tissues, toothpicks, bottles, bed linens, or any item that may contain traces of DNA. These findings are placed in paper bags and transported to a lab through a chain-of-custody procedure. This ensures that the evidence will not be intercepted and switched at any time on its way to the testing facility.
Once the DNA artifacts arrive that the forensic laboratory, they will undergo analysis. There is many ways that these tests are conducted. A restriction fragment length polymorphism of (RFLP) analysis analyzes the length of the strands that include the repeating base pairs. Then they categorize these variable tandem repeats (known as VNTRs.) To do this analysis, inspectors need a large sample of DNA that has not been contaminated, so this is not always the most practical inspection process.
Other times, labs conduct a short tandem repeat analysis or a STR. This method requires a smaller sample of DNA and uses a polymerase chain reaction to analyze. To conduct a STR, the forensic investigators look to see how often pairs repeat at a specific loci on a DNA strand. The Federal Bureau of Investigation has chosen 13 of these loci as the standard for DNA analysis. The change that two individuals could receive matching results from an STR is one in one billion. There are also some specialized techniques that can be performed on DNA like Y-marker analysis (for sexual assault cases), mitochondrial DNA analysis (for cold cases), and single nucleotide polymorphism (for further investigations.)
When the DNA analysis is completed in the lab, suspects' DNA is matched with the laboratory results. Those who match are considered "inclusions," and those who don't are discounted as "exclusion." If the case at hand involves no subjects, then investigators may want to compare their data to other DNA profiles which are held in a state database. This is known as the State DNA index system, and contains DNA profiles of convicted offenders. If the state archive does not reveal the needed results, the National DNA Index System can broaden the search. The Combined DNA Index System is software that investigators use to run searches on DNA at the national level. This new computer database has helped solve many cases by giving researches the "cold hints" they need to solve a case.
While this way of testing has become a helpful and beneficial crime scene investigation method, it isn't always reliable. Every once and a while a confusion in DNA or a laboratory mix-up can completely reverse a court case, and point to innocent individuals as the offenders. Items at the crime scene that were used as evidence may be unrelated to the case, and point to the wrong person. If you have been falsely accused of a crime, you need to speak with a lawyer immediately and start proving your case.
