CSI And DNA
What is DNA and how is it used in CSI?
DNA stands for deoxyribonucleic acid, and it is the most significant advancement in forensic science during the past 15 years. The importance of DNA is its ability to link an individual to an item of physical evidence with near-absolute certainty, if not absolute certainty. Anything that an individual may have touched, whether with his or her hands or lips, is a possible candidate for DNA analysis. So investigators at crime scenes must be on the outlook for these items of physical evidence. That has certainly changed the complexion of crime scene investigation in the past 15 years. But it's the link between biological evidence and an individual that can be made with certainty that is the key to understanding the significance of DNA evidence for all investigation today.
When was DNA first used in CSI?
What effect did the 'Colin Pitchfork Case' have on DNA use in CSI?
The Colin Pitchfork case is, to my knowledge, the first documented case where DNA was used in the investigative process. In 1984, Alex Jeffries discovered the applicability of DNA to forensic analysis. Shortly thereafter the police undertook the investigation of a double murder in a town in England, and ultimately voluntarily collected biological specimens for DNA analysis from all the residents of that town. As a result of the DNA analyses that were conducted, Colin Pitchfork was identified as the perpetrator of the crime. Now, interestingly enough, as a result of DNA analysis, it's also the first known instance where a suspect was exonerated for the commission of a crime, because that is exactly what happened in the Colin Pitchfork investigation.
What process is used to collect DNA for CSI?
From a human being, DNA is collected either through a blood sample or through a mucal swab, that is swabbing the inner portion of the cheek with a cotton swab. As far as evidence at crime scenes, any blood stain or any semen stain is certainly a candidate for DNA analysis. There are other things that may contain DNA that may not be as apparent, such as a cup that has become in contact with saliva, or a cigarette butt that has come in contact with saliva. There are lots of what we call carriers of DNA that may not be very apparent to the investigator at the crime scene, and that's why a thorough collection of these items must be made and brought back to the lab for further investigation and analysis for DNA.
How is a PCR DNA test done for CSI?
PCR stands for polymerase chain reaction. That really revolutionized forensic DNA analysis. With the advent of PCR, which came about in the 1990s, the forensic scientists were able to duplicate or replicate DNA to the point where we can detect maybe 18 or so cells. Just think about that, 18 cells are generally required for a DNA analysis, and that is due to the fact that PCR is, we call it a Xeroxing or replication where it takes a very small amount of DNA and just keeps multiplying it. And that's what's giving rise to the tremendous sensitivity associated with DNA analysis. PCR is the wonder technology of the crime lab of the 21st century.
What role has DNA played in reopening old criminal cases?
There have been well over 200 individuals in the United States that have been exonerated (convicted individuals) through the use of DNA. It's just that back in the 1980's and the 1990's, many investigations relied solely on eye-witness testimonies and confessions. These were obviously devoid of any scientific evidence. However, even without scientific evidence, juries still convicted people. In many of these cases, the evidence has been preserved, and this has allowed scientists to go back and reopen these cases and look at the DNA aspects of the case. And that's one of the beauties of DNA. It's pretty hard and it will stay with us, along with the evidence for very long periods of time. Thank goodness for that, because there are well over 200 individuals that have their freedom to thank for DNA, or to DNA.
How was DNA used in the investigation of the Clinton and Lewinsky case?
There was a semen stain that was found to be present on a dress that is owned by Monica Lewinsky. She claimed that stain belonged to President Clinton. Ultimately, her dress was retrieved and was sent off to the FBI laboratory where it was analyzed by the technology used back then, RFLT, and the result showed the association of that stain with Bill Clinton was about seven billion in one.
