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Though we all may have an idea as to what DNA is, most only picture the double helix when they hear the word. DNA, or Deoxyribonucleic acid, is more then just a 3D image of the latter-like double helix we see in magazines and on television. It is fundamentally the building blocks of life. DNA contains all of our genetic material from which all of our physical, mental and emotional characteristics come from. Though there are many studies of DNA, we still do not have a full understanding of all of its components. However, in the past decade, leaps and bounds have been made in this field of study and many applications of this knowledge have been discovered; such as the use of DNA in criminal investigations. DNA evidence had been a key component in criminal investigations since the discovery of its promising uses during the 1980’s. DNA can be the most concrete piece of evidence in an investigation and it can mean the closing of a case. DNA is also important in building a case, and while the presentation of it during a trial is the ultimate goal of an investigation, the actual collection of the evidence, along with its analysis and preservation, is the most important and critical period during the entire process. Also, controversy is entwined in the use of DNA, many arguing both for and against its different uses.

When a crime is committed, the first priority is securing the scene, unless there is an emergency and victims need immediate medical attention. However, barring any sort of medical emergency, those who first arrive are to block off the scene to prevent any evidence from being destroyed or contaminated. After the scene is secured, forensic scientists are called in to ‘process the scene’, which generally means to collect evidence, document and photograph the entire scene. This is important because an accurate record of the scene will help when trying to reconstruct the crime. After properly documenting the scene, the forensic scientists then begin to thoroughly scour the area to find any physical evidence. Physical evidence refers to any DNA evidence such as hair, blood, tissue or body fluids that have been left behind. To ensure all evidence is found, there are a few different techniques to help reduce the risk of any traces being left unfound. 

The Zone method of examining a scene is usually one of the most common search and securing methods implemented for indoor crime scenes. Houses or structures are usually searched in a room-by room basis then each room is further divide into smaller sections. Each section is then thoroughly combed for any trace of evidence that may point the investigators in the right direction that will eventually lead them to a suspect. (Nickell and Fischer)

The Grid method, another searching process, is mostly used for outdoors but may include large areas such as the inside of a warehouse or other open areas indoors. In this method, the searchers section off the area in parallel rows and search each section until the entire area is covered. The searchers cover the area again, in a perpendicular pattern until they have covered the entire area a second time. A great deal of care is taken in searching the crime scene, so that there is little to no chance of a piece of evidence or clue being missed. This almost always ensures that the crime is accurately reconstructed. (Nickell and Fischer)

While searching crime scenes, the investigators must always take great care in preserving the evidence they find. The preservation of evidence is the most important and crucial part of the entire criminal investigation. Contamination of evidence is the one thing that can bring a case and its conviction crashing to its knees. To ensure that this doesn’t happen, two things can be done. One is proper handling and labeling of evidence collected at the scene. There are proper procedures for the many different types of physical evidence to ensure its preservation. Trace evidence, such as hairs, fibers, dirt and other evidence collected in minute particles are to be placed in bottles with secured lids and/or wrapped in filter paper and placed into a pill box. Any collection of hair or fiber trace usually occurs through a vacuuming collection system. Paper, either documents or pieces with fingerprints are never to be folded, but are too be placed into cellophane envelopes. Any stains of interest found on a piece of clothing are to be circled in chalk, then folded with white paper carefully inserted between stains to prevent contamination and placed into a sterile box. Any weapons are to be secured to a board with string unless fingerprints have already been lifted. If the weapon found has already been printed, then it may be wrapped in a cotton cloth and placed into a box for transportation. There are many more protocols that are strictly enforced to reduce and even eliminate the chance of cross contamination. Another way to stop any problems with DNA confusion and contamination are control samples. Control samples are very important, especially in cases such as physical and sexual assault with evidence being collected from the victim’s body. A control sample is usually a piece of foreign material that may have contaminated a piece of evidence. These control samples help with the separation of DNA evidence so no confusion occurs during processing and identification. (Zonderman)

Once evidence has been collected, it must be taken to a forensics lab to be analyzed. The different types of trace evidence, such as fibers, hairs, blood, and others are each analyzed in different ways. Blood is usually analyzed in a process known as serology. This process is also used in many other types of analysis involving any type of biological material which can include saliva, perspiration, seminal and vaginal fluid and any type of human tissue. Once the materials have been gathered and are prepared for testing, preliminary tests must be done on the material to prove that it actually is a biological material. It would be a waste of both time and funding to perform complex tests on a suspect material only to find that it was not a biological material critical to the criminal case. Once it is established that the material is actually blood, a serologist will then identify its blood type. Determining a positive blood type is then enough cause to perform DNA typing on the material. Once a DNA profile is made, the results may then be run through a criminal database and from there suspects may be found or confirmed.

In the beginning, when DNA was first used to get a ‘DNA fingerprint’, the forensic scientists used a procedure called Restriction Fragment Length Polymorphism Analysis or RFLP analysis. In this technique, the DNA that is to be analyzed is cut into short sections by an enzyme that is specially selected. This enzyme is will cut the DNA according to the repeating sequences in each piece of DNA. Every person’s individual DNA will have these repeating sequences that are unique to that person. After the enzyme cuts the DNA, the resulting fragments are then separated according to size, which is achieved through negatively charging the DNA fragments. Once the fragments are arranged according to size, the end product is then soaked in a sodium hydroxide and sodium chloride solution. This process will separate the double stranded DNA that was started with, and it will become a single stranded DNA. Then, a probe with a florescent or radioactive substance material is then bound to the single strand DNA to allow for visualization. The pattern of DNA will then be able to be used for DNA identification. (Andres)

As unfortunate as it is, most cases involving blood evidence there is usually an abundance to collect and analyze. However, in the event that blood, or any type of DNA evidence, is very minute there are processes that can be used to make that trace evidence the amount needed for identification. Once such process is the Polymerase Chain Reaction; or PCR for short. In this process, forensic scientist takes the microscopic amount of trace evidence, called a template, and adds it to a mix of reagents and a buffer. Then in timely process of thermal treatment, a continual cycle of heating a cooling, the four main strands in a DNA sequence are separated and reconnected. This expands the amount of DNA that the forensic scientists have to work with, making it possible to make use of even a piece of evidence the size of a pinhole. (Andres)

While hairs and fibers are to all appearances very similar, they are in fact quite different. Fibers are usually classified as both natural and man-made. A natural fiber would be cotton or wool, while a man-made fiber would be polyester. Hairs are defined as an appendage of a human or animal which grows from the skin. When a fiber or hair trace is found at a crime scene, it is sent to a forensic lab to be examined by a forensic expert to determine its characteristics. DNA cannot be pulled from a hair follicle, though if the hair root remains on the follicle, DNA may be extracted. Hair is an excellent piece of evidence and considered very valuable, in lieu that it resists both natural and chemical decomposition. It can also retain all of its characteristics for years. Hair follicle evidence is important because it may reveal the donors race, and may also reveal tentative results as to gender and age. When being analyzed, forensic experts look at a number of things including but not limited to color, length, diameter, the tip, the base, the root (if present), pigment, cuticle and scales. Once the results are completed, one of three things can be concluded. One, that all samples collected are consistent and came from the same donor;  two, that the samples did not correspond with each other and therefore did not come from the same donor; or three, the results were inconclusive. (Nickell and Fischer)

Fibers, it may seem surprising, are actually considered better evidence then hair follicles. They are considered more valuable because of the numerous variables they may contain. Variables such as the number of fiber in each strand, strand diameter, twist, weave, dye color and content, along with any other type of foreign material that may be imbedded inside the fiber are all very important. To view the strands so that this valuable evidence may be collected from them, electron microscopes and photo-micrographic microscopes are used to magnify the fibers by 100x, enough to see distinctive features that may be valuable evidence. (Zonderman)

All of the processes used to identify any and all trace evidence from the scene of a crime are to reach one goal, building a case that will bring a conviction. When all trace evidence has been analyzed, the result will usually confirm or identify a suspect, through the use of criminal databases. DNA is believed to be the best type of proof that a suspect is indeed the perpetrator. ‘Hard evidence’ as it is called, or physical evidence refers to any type of tangible object, for example hairs, fibers, or blood evidence. This hard evidence is what usually tips the scales towards a conviction.

With all of our technological advances, DNA is also being used to solve older cases, or ‘cold cases’ that were unable to be solved just a few decades ago from lack of evidence. Reexamination of the evidence of these cases usually brings up new evidence that provides more clues into the crime. Many cold cases have been solved because of DNA typing and analysis. For example, in 1979 22-year old Janet Chandler was the victim of sexual assault and murder. Though an investigation happened, there were few leads at the time. Her killers were never found. Then, 20 years later, a cold case team reopened the case and pieced all of the evidence back together. In 2007, almost exactly thirty years later, five men and a woman were tried for her murder and of those four of the men were found guilty and sentenced to life in prison. Though the punishment was long in coming, justice won in the end with the use of new technology. This is example is just one of many cold cases that have been solved through the use of new forensic technology. (Gomez)

 Moreover, DNA evidence is now being used to bring about exoneration, overturning wrongful convictions and giving back freedom to innocent people. One of the most resent cases that were found to be a wrongful conviction was that of Byron Halsey, who was wrongfully convicted and sentenced in 1985. He spent seventeen years in prison for the murder of two children before his case was reexamined. It was then found, through DNA evidence that Halsey was not the killer. In 2002 the real perpetrator was found and Halsey was released. Through a new program, the Innocents Project, hundreds of cases are being reexamined and the evidence reviewed. Since 1989, there have been around 200 hundred convictions nationwide that have been overturned, 14 of which were innocent people who had been sentenced to death. Though the types of conviction that can be exonerated through DNA evidence are limited to sexual assault or sexual assault/murder and murder cases in which an unknown DNA donor is involved, more avenues are being explored to expand this group. (Taylor Jr.)

DNA evidence in the criminal justice system is also the subject of much controversy. There are two subjects that are the topic of particularly heated debates: DNA databases and wrongful conviction. Though DNA databases are main parts of criminal investigations, many do not like the fact that such personal information is on file, even though the files are only used in DNA identification. A very common argument in favor of keeping and expanding DNA data bases is that only those who have committed crimes have anything to worry about. Only those who have been convicted of a crime are left in criminal databases and according to policy, those who have been suspect but cleared are to be deleted. People exonerated are also to be deleted from the databases. (Jost) Yet people still argue over the privacy issue. Another point of argument is wrongful conviction, and this topic goes back to the margin of possible error during processing and even contamination of evidence. While human error is a possibility in the collection, analysis and processing of any and all DNA evidence, this margin is quite small. Everyone who handles the evidence checks and rechecks that everything has been done correctly.

DNA, now, is one of the most important building blocks of a successful investigation today. Since its importance and multiple uses were discovered, the uses of DNA evidence have expanded. Using DNA in a criminal investigation is one of the most important uses of DNA in this modern era. Though we do not have a full understanding of the potential of DNA, what we know and understand now is of great value. DNA can be used to build a case, get a conviction or overturn a wrongful conviction. While each component of an investigation is vital, DNA is an important facet in the entire investigation process.

 

 

References

 

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