Collection and preservation of DNA


The world of forensic science is progressing every seemingly everyday. The technology is so complex and cutting edge that it is imperative for constant revisions to the common knowledge of the science amongst its practitioners. However, the history of collecting evidence spans throughout the history of human existence in the form of fingerprints in paintings and rock carvings (Evans, 1996). It is understood from their inclusion on these media platforms that early humans knew that the fingerprint was an identifier of the individual. It has been documented that since the 700s, the Chinese used fingerprints to authenticate documents. About the year 1000, Quintilian, A Roman attorney, won acquittal or his client by proving that bloody palm prints were intended to frame him (Bennett, 1998). For roughly another 1000 years 'forensic' science was very macroscopic and physical in nature. In 1986, the first DNA evidence was used to solve a crime of the murders of two girls in the Midlands of England. The collection and preservation of DNA evidence is a very sophisticated, controlled, and evolving process. Proper collection and preservation, or the contrary, can have profound impacts on the persons involved. My research aims to focus briefly on the history and process of systematically processing crime scenes and the proper collections and preserving of volatile DNA evidence.

Protocols and Crime Scene Processing

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Long before the primary aim of crime scene investigators was to gather suspected evidence that contained DNA evidence the process of overall crime scene investigation was evolving. As aforementioned in the introduction, evidence has existed the moment humans have existed. The goal of evidence collection is to eliminate contaminating said evidence. In an effort to do this forensic scientists typically follow a crime scene protocol when collecting or preserving evidence. Upon the landmark proclamation of Dr. Edmond Locard in 1920 that "every contact leaves a trace," there was a movement of implementing a crime scene protocol at the local level (Ragle, 2002). Crime scene analysis began by policing bodies as a paradigm of searching, note taking, collecting and preserving physical evidence. It has sense continually evolved into a complex, slow, methodical, systematic, and orderly process that involves several protocols intertwined and a processing methodology. Far too many investigators cave into pressure to get the scene working and functional again, especially if it is an area of commerce. Having a method or game plan protects against charges the scene was ransacked or blundered. In fact, some police departments now require an onlooker to sign up as civilian monitor (Ragle, 2002).

The current protocols do everything to ensure the crime scene and its contents are secured. It has been received as such a necessity that there is legal litigation concerning the matter. It is now known that the preservation of evidence is secondary only to an emergency situation. A crime scene emergency exists only when officers reasonably believe that a person inside needs medical attention or there are other victims or perpetrators inside (Mincey v. Arizona, 437 U.S. 385, 1978).

In researching I found that the new literature and evolution of protocol speaks to stabilizing a crime scene. Most textbooks emphasize that a first responder's duty includes first aid. The answer no one wants to talk about is no, not right away. The only times a responding officer should rush into the scene is when someone is laying there, in your opinion still alive (breathing), moving, and/or reaching for a gun.If the victim is harmed and still alive, an attempt should be made to take a dying declaration. EMS and fire personnel are trained to sensibly enter crime scenes so that they follow a safe pathway which is where the least evidence is disturbed. If possible, the responding police officer should try to find the suspect's and victim's entry and exit points, and direct emergency personnel to enter and exit at another point, or via a pathway the officer has already established in a check for signs of life. Any of these kinds of emergency actions should be documented in notes, or better, with a crime scene log that has been set up. Every effort should be made not to disturb the crime scene, and preserve it in as pristine a condition as possible (Sonne 2006.)

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There is rarely more than one opportunity to obtain evidence from a crime scene, the investigation by the crime scene investigation must be methodical and complete systematic steps. Hollywood has made it seem so simple; but in fact crime scene processing is a very intricate and interwoven multiple task function. It is difficult to explain the exact protocol that will be used at every crime scene. Each crime scene is different and may require a different approach to processing the scene. However, there is a basic crime scene protocol that should be adhered to in all crime scenes. These basic functions or tasks are to secure the scene, conduct interviews, examine, photograph or videograph, sketch, and process the scene.

Securing the crime scene is making certain that it is safe and well, secure. This critical first step involves also establishing a log which is used to document who enters and leaves the scene and the evidence they may touch or remove. Conducting interviews is the second step in the typical processing of a crime scene. The crime scene technician must interview the first officer at the scene or the victim to ascertain the theory of the case. Basically, what allegedly happened, what crime took place, and how was the crime committed (Barry, 2004). This information may not be factual information but it will give the crime scene technician a base from which to start.

Thirdly the protocol involves examining the crime scene. This is done to ascertain if the theory of the case is corroborated with the evidence at the scene. The examining step in the protocol allows for the identification of possible items of evidentiary nature, identify point of entry and point of exit, and getting the general layout of the crime scene.

The fourth step of the general protocol is to sketch, photograph, and videograph the scene. I lump these together as they work as pieces of a collective step that involves providing an accurate portrayal of the scene. As learned in my summer studies with Larry Barksdale this step aims to record items of possible evidence. It is common place that this step includes overall views and close ups (Barksdale, 2009).

The last step in the protocol is to process the crime scene. Process the scene for what? The crime scene is processed for evidence, both physical and testimonial. It is the crime scene technicians' responsibility to identify, evaluate and collect physical evidence from the crime scene for further analysis by a crime laboratory. Scientific and technological advances have resulted in the development of laser and alternative-light sources that can reveal latent fingerprints, stains, hairs, fibers, and other trace evidence (Fisher, 2004).

Collection and Evidence as it relates to DNA

In keeping with Locard's exchange principle, crime scene investigators collect evidence from the crime scene that may have been touched or microscopically "contaminated" by the suspect or suspects. They also take samples of fibers, dirt, and dust in hopes of finding traces of serological evidence that may be used in an attempt to determine the parties associated with the evidence.

The beginnings of DNA as a crime scene tool is in Germany in 1900 when Karl Landsteiner discovered human blood groups which incidentally laid the foundation for future forensic science evidence. The Italian scientist, Leone Lattes in 1915 developed the first antibody test for ABO blood groups, which he almost instantly applies to criminal investigation. The Japanese scientist, Saburo Sirai discovered secretions of group-specific antigens into body fluids other than blood in 1925 (Evans 1996). With the development of Luminol in 1937 and the development of the acid phosphatase test for semen evidence in 1945, forensic science was gaining strength and notoriety as a science academically, and as tool in legal matters. Of course Watson and Crick identified DNA's structure in 1953. After their revelation, hundreds of researchers and scientists improved on our understanding of DNA and its power as an individual identifier.

While the technology and methods of identifying bodily fluids, identifying, and processing DNA progressed, it wasn't until 1984 when Sir Alec Jefferies of England developed the first DNA profiling test (Evans 1996). The United States courts admitted DNA as evidence in the conviction of Tommy Lee Andrews in a series of sexual assaults in Orlando, Florida. The rest as they say is history. DNA evidence is now one of the strongest pieces of evidence a crime scene can produce if the court is confident that it was collected with proper care as to eliminate any reasonable chance of contamination. Scientists have since established laboratories that process evidence in a very accurately fashion. Many man-hours have been spent on identifying introns and exons in the DNA sequence as part of the human genome project.

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Our understanding of DNA has increased with the development of several techniques. One such technique is, Agarose Gel Electrophoresis; which is a technique forensic scientists use to compare the size of certain strands of DNA of two samples. It works by passing a current through the gel that contains DNA from the crime scene. The DNA will be drawn to the opposite end of the agarose gel as it is attracted to the opposite charge. By comparing the sample from the scene to that of a suspect it can be determined if the party was present and even perhaps guilty.

The development of Polymerase Chain Reaction techniques, that increase the quantity of DNA material have, added to the likelihood that the DNA material will be of use in the investigation. Short tandem repeats and thermosequencing has done a great deal in reducing the cost and complexity of DNA sequencing.

The protocol involving DNA evidence has been revamped and revolutionized to reflect new research findings and trials. The process entails much more documentation to discredit defense attorneys who claim that evidence was planted. The chain of custody has received a great deal of attention in the process of an investigation since the O.J. Simpson trial (Ostrowski, 2009). The kits and methods of analyzing the kits has become so consistent and strong that the only piece left be debated is the likelihood of contamination by a member of the investigation team or laboratory. The process also calls for the evidence to be obtained and refrigerated or frozen as expeditiously as possible (Lee, 2008). While there are techniques to help determine the origin or degraded evidence the forensic community would concur that the more usable sample available for analysis, the better.

DNA collection and preservation techniques are effective if done properly. The strength of the evidence and it's utilization as a legal tool comes from the reputation of those involved in its handling (see O.J. Simpson).


  • Barksdale, L. 2009. Forensic Photography Lectures. UNL, Lincoln, Nebraska.
  • Bennett, W. 1998. Criminal Investigation. Fifth edition. Wadsworth, Belmont, California.
  • Evans, C. 1996. The Casebook of Forensic Detection. Wiley, New York, New York.
  • Fisher, B. 2004. Techniques of Crime Scene Investigation. CRC Press, Boca Raton, Florida.
  • Lee, H. 2008. Collection and Preservation of DNA Evidence. Promeda, New Haven, Conecticut.
  • Ostrowski, R. 2009. Interview. UNCC, Charlotte, North Carolina.
  • Ragle, L. 2002. From Fingerprints to DNA Testing- An Astonishing Inside Look at the Real World of C.S.I. New York. Avon Books, New York, New York.
  • Sonne, W. 2006. Criminal Investigation for the Professional Investigator. CRC Press, Boca Raton, Florida.