"Oh what a tangled
web we weave, when first we practice to deceive."
Sir Walter Scott
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web we weave, when first we practice to deceive." |
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Michal Schwartz is currently pursuing the M.S. in Forensic Science from the College of Criminal Justice, Sam Houston State University. Richard C. Li is Assistant Professor of the College of Criminal Justice at Sam Houston State University. Direct correspondence to Prof. Li at the College of Criminal Justice at Sam Houston State University. |
Forensic science aims at linking a suspect to the crime by employing scientific methods to analyze evidence. Forensic DNA analysis has become one of the more widely known ways to prove a suspect’s guilt or innocence, specifically in violent crimes such as a rape or murder case. The most popular forms of DNA evidence come from blood, saliva, semen, and hair samples. When such violent crimes occur, those samples of evidence could be collected for forensic DNA analysis.
A good example of a property crime that may call for forensic investigation is burglary. The victim of a burglary, though physically unharmed, feels violated and unsafe. What people do not always realize is that burglars also leave their DNA behind, just in a less obvious way. Technically, when someone touches an object he leaves traces of his own DNA behind. Everyone sheds DNA through the sweat of his hands; however, the amount that is left is so small as to be undetected, normally. Moreover, virtually any body surface will shed trace amounts of DNA. This fact provides endless possibilities for collecting evidence at scenes of property crime. For instance, if a burglar pressed his ear against a door before entering, his DNA may be left on the door. If he accidentally pressed his lips against a window while opening it, his DNA may be on the window. Finally, any articles of clothing he may have had on, especially the gloves he wore to cover up his fingerprints, may yield DNA evidence (if the investigator is lucky enough to confiscate them).
Current methods of forensic DNA analysis involve a technique called polymerase chain reaction, or PCR for short. PCR amplifies a small fragment of DNA in a series of cycles so a greater amount of that same DNA is available for analysis. Using the PCR method, the number of DNA copies is increased to the point where over millions of copies are produced. From there the forensic scientist can accurately identify the specific DNA markers which set that individual apart from the rest of the population. This is why DNA typing is often referred to as “DNA fingerprinting.” Like a person’s own handprint, his DNA is unique. Upon analyzing the DNA found at the crime scene, DNA taken from any suspect is analyzed in the same manner. If the suspect’s DNA profile matches that of the crime scene sample, then strong evidence exists of a linkage between suspect and crime scene.
PCR technology was already an improvement in the area of forensic DNA analysis, as it allowed for analyzing DNA samples of limited quantity. Since its development in the mid-1980s, conventional PCR can successfully amplify DNA from, for example, less than one drop of blood. The late 1990s brought another advancement, namely Low Copy Number (LCN) DNA.
LCN DNA is a technique that employs the same kind of analysis of a PCR product; however, it can amplify an even lower quantity of DNA sample. In this way even trace amounts of DNA found at a crime scene are detectable. Thus LCN DNA, if adopted into regular forensic laboratory practice, will provide the solution to detecting the minute DNA samples left behind in property crimes.
The methods for collecting DNA evidence are just as important as the methods of its analysis. Our laboratory, together with the Department of Forensic Science at University of New Haven, has recently developed a new DNA collection method that employs adhesive tape for collecting DNA samples. The use of adhesive tape to remove skin cells produces a dry sample that would be well protected from air, moisture, and other potential contaminants. The resulting sample can be conveniently stored until needed, during which time a small portion may be cut from the tape for processing. Our studies found that forensic DNA analysis was successfully performed on the skin cells collected using this adhesive tape method.
The potential applications of this collection method are currently being explored. Studies are still being conducted on the possible evidence sample collection techniques. Examples of possible physical evidence samples include porous surface materials (e.g., hatbands, shirt collars, and other garments), smooth surfaced materials (e.g., firearms, weapons, tools, and cuffs), and fingerprints.
The application of this method provides a new and potentially valuable method for collecting DNA samples for forensic DNA analysis. As indicated above, we have learned that the adhesive tape removes and preserves skin cells for successful DNA analysis. This collection method should reduce the risks of DNA degradation due to bacterial action, which are encountered when using conventional collection methods. Additionally, the proposed method should increase the yield of DNA isolation from samples which contain limited DNA. The improved yield of DNA isolation will raise the success rate in generating DNA profiles for forensic DNA analysis. This would have a significant impact on forensic DNA identification, thus benefiting the criminal justice system as a whole. This method could provide new investigative leads for various criminal cases like cold cases and property crimes such as theft and robbery.
References
Li, R.C. & Harris, H.A. (2003) Using adhesive tape for collection of evidence for forensic DNA analysis. J. Forensic Sci. 48:(6)1318-21.
Rudin, N. & Inman, K. (2002). An introduction to Forensic DNA Analysis. 2nd Edition, CRC Press, Florida.
Wise, J. & Li, R.C. (2003) The Future of DNA Evidence. Crime & Justice International 19:(70) 31-32.
Copyright 2005 by Michal Schwartz and Richard C. Li
| "Oh what a tangled
web we weave, when first we practice to deceive." |
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| W M M New Issue | W M M Archives |