The Importance Of Dna Evidence
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The Importance of DNA Evidence
What is DNA? Is it these winding strands that look like ladders or is it what gives a person blonde hair and blue eyes? Actually, DNA is both of these things. DNA is a person’s genetic makeup—their hereditary blueprint passed on by their parents. It is a part of almost every cell in the human body. In each cell, a person’s DNA is the same; it stays the same throughout their lifetime. DNA is found in skin tissue, sweat, bone, the root and shaft of hair, earwax, mucus, urine, semen, and vaginal or rectal cells. The DNA found in a person’s saliva is the same as the DNA found in their blood. Parts of the DNA determine our physical characteristics, such as eye and hair color, height, and bone structure, but the DNA collected from the crime scene is for evidentiary purposes only and not to determine an assailants physical characteristics. (Turman)
Originally, DNA profiling was developed as a method of determining paternity. Samples taken under clinical conditions were examined for genetic evidence that could link parent to child. DNA evidence was first introduced to courts in England in 1986, when a molecular biologist was asked to verify the confession of a suspect. Alec Jeffreys, the molecular biologist, had begun investigating the use of DNA forensics and aided English police in excluding a 17 year-old boy as a suspect in two rape-murders. The tests proved the teenager was not the perpetrator and the actual attacker was eventually caught, also using DNA testing. In the United States, the first DNA-based conviction occurred in 1987 when Tommy Lee Andrews was convicted of rape by the Circuit Court in Orange County, Florida. Andrews’ DNA test from a blood sampled matched the DNA of semen traces found in a rape victim. Two years later in West Virginia, the first state high court ruled in favor of admitting DNA evidence. (Cormier)
In criminal investigations, DNA has proven to be a powerful tool. Since no two people, excluding identical twins, have exactly the same DNA, it can be used as evidence in a criminal investigation to identify suspects, convict the guilty, and exonerate the innocent. DNA can also identify a victim through the DNA comparison of a relative. This can be helpful in cases where a victim’s remains are not found. For example, technicians can use biological samples, such as a bloodstain from a victim, found at a crime scene and compare the DNA from the bloodstain to the DNA of a victim’s biological relative. This can conclude that the bloodstain at the crime scene belongs to the victim because DNA is hereditary. When a DNA profile developed from evidence at one crime scene is compared with a DNA profile developed from evidence found at another crime scene, they can be linked to each other or to the same perpetrator, whether the crime was committed locally or in another state.
DNA evidence such as saliva, blood, skin tissue, hair, and semen are most often recovered from crime scenes and can be crucial to the investigation of sexual assaults and other violent crimes. For example, during a sexual assault, biological evidence such as hair, skin tissue, semen, blood, or saliva can be left on the victims body or at the crime scene. In addition, hair and fiber from clothing, carpet, bedding, or furniture could be transferred to the victims body during an assault. This evidence is helpful in proving that there was physical contact between an assailant and a victim. DNA properly collected from the victim, crime scene, or suspect can be compared with known samples to place the suspect at the scene of the crime. If there is no suspect, however, a DNA profile of the crime scene can be entered into the Federal Bureau of Investigations (FBI) Combined DNA Index System (CODIS), which allows agencies to match DNA profiles with other profiles entered into local, state, and national databases to identify a suspect or link serial crimes.
CODIS is a computer software program that operates local, State, and national databases of DNA profiles from convicted offenders, unsolved crime scene evidence, and missing persons. Every State in the Nation has a DNA database that allows for the collection of DNA profiles from offenders convicted of particular crimes. CODIS software enables State, local, and national law enforcement crime laboratories to compare DNA profiles electronically, thereby linking serial crimes to each other and identifying suspects by matching DNA profiles from crime scenes with profiles from convicted offenders. The success of CODIS is demonstrated by the thousands of matches that have linked serial cases to each other and cases that have been solved by matching crime scene evidence to known convicted offenders.
Recent advancements in DNA technology have improved law enforcement’s ability to use DNA to solve old cases. Original forensic applications of DNA analysis were developed using a technology called restriction fragment length polymorphism (RFLP). Although very old cases (more than 10 years) may not have had RFLP analysis done, this kind of DNA testing may have been attempted on more recent unsolved cases. However, because RFLP analysis required a relatively large quantity of DNA, testing may not have been successful. Similarly, biological evidence deemed insufficient in size for testing may not have been previously submitted for testing. Also, if a biological sample was degraded by environmental factors such as dirt or mold, RFLP analysis may have been unsuccessful at yielding a result (Turman).
Although DNA technology can be used in criminal cases to place a suspect at the scene of a crime, it also can be used to solve cases where no suspect previously existed. Using new technology to analyze DNA evidence in old cases can provide answers to questions of guilt and remove lingering doubts.
In 1990, a series of brutal attacks on