OBTAINING and RECORDING PHYSICAL EVIDENCE
When it comes to identifying people that have committed a criminal act, the most positive means is through fingerprints. When we are born, our fingerprints stay with us until we die and our bodies start decomposing. To the human eye our fingerprints look the same, however, further investigation will show that each of us have a unique set of friction ridges that comprise our fingerprints and sets our identity apart from each other. At a crime scene, there are two different types of fingerprints that may be found. Patent prints are visible to the human eye. Latent prints are “unintentional prints found on items of evidence or at a crime scene” (Unknown, Obtaining and Recording Physical Evidence, n.d.).
The ability to visualize prints depends on the physical condition of the person who left the print, the surface on which they left it, and the reflection of the light which is used to help visualize the print. Other circumstances that effect the visibility of latent prints is time and exposure to elements like heat and cold. However, in any case, prints should be attempted to be obtained. When latent prints are smudged they lack the specific ridges to distinguish the print correctly. These types of prints may not be perfect for fingerprint analysis; they may be utilized to provide other trace evidence.
Before latent prints can be lifted and processed they need to be discovered. Each print left in different types of surfaces have to be processed in a special way. The most common means is with the use of fingerprint powders or through chemical treatment. Most field kits supply a variety of colors so that the powder can contrast with the background on which they were left. The most widely used colors are black and white because they are standard colors that contrast on many objects.
Fluorescent fingerprint powders help develop prints on multicolored surfaces, and require the source of ultraviolet light. As with most equipment, safety goggles and gloves should be used to avoid undue exposure and harm to the investigator. It is important to have a delicate touch and a small amount of powder to make the latent print visible. Once the print has started to show up, continuing to brush with the direction of the friction ridges will make the fingerprint stand out. At that time, a photograph of the print should be taken and logged prior to lifting the print. If an investigator is in the field without proper powders, passing non-flammable evidence through the smoke of a burning piece of pine will cause soot to deposit on the object.
Chemical processing of latent prints happens in the laboratory. Lab technicians are trained in using techniques that are required by the federal law in using many chemical mixtures to aid in processing evidence. Many porous objects will absorb the secretions from fingerprints and will not rub off as easy as they will on nonporous surfaces or objects. In order to get these prints visible, chemicals are applied to react to the secretions to make the print visible. The amount of contact and pressure applied by the fingers will affect prints the most.
Once the prints are visualized, and photographs have been taken, prints can be lifted and placed on a print card and transported to the lab for further processing. The most common method to use for lifting prints is rubber lifters and transparent lifting tape. Rubber lifters work the best on curved or uneven surfaces, whereas transparent tape will lift the print in the position in which they were left on flat surfaces.
How to Lift Fingerprints
The basic police officer’s fingerprint kit should contain a fingerprint brush, black and bi-chromatic powder, lifting tape, and fingerprint cards. There are several types of fingerprint brushes available, the one to use is a personal preference. Fiberglass fingerprint brushes have a better rate of to “distribute the fingerprint powder evenly” (Spraggs, 2007).
Most crime scenes will utilize the black lifting powder; however, the bi-chromatic powder will be very helpful in processing prints on dark surfaces, because it is a mixture of the black powder with a white or silver powder. When the bi-chromatic powder is used on dark surfaces it will look light and it will show up dark on light surfaces.
The best rule for processing latent prints using powder is to use less lifting powder than you think you are going to need. Many latent prints can be ruined by over processing with powder. David suggests “give the print powder jar a quick shake before opening the lid” then goes on to say “remove the lid and place the fingerprint brush inside the lid” (Spraggs, 2007). The lid will retain enough powder to start processing the latent print. A precise amount of pressure applied while spinning the brush will produce a good print with good ridge detail. He mentions that too much powder will fill the ridges and over process the print and too little will not produce enough, keeping in mind that too much contact between the brush and the print will damage the print.
Once the print has been developed it is time to begin lifting the print. Lifting tape comes in a variety of widths and compositions. General lifting tape is used on flat surfaces and polyethylene tape is great for curved surfaces like door knobs. An important key in applying the tape is to keep it evenly and as smooth as possible. David suggests using a credit card to ensure even and smooth applications. “Securing the lifting tape about an inch from the edge of the print, then use the edge of the credit card to gently press the fingerprint lifting tape onto the surface” (Spraggs, 2007). This process allows for thorough adhesion of the powder and the tape ensuring that air bubbles are eliminated at the same time and being trapped in the tape. He also utilizes the credit card again when placing the tape to the fingerprint card.
How Far Should Prints Be Trusted?
Fingerprint analysis is not an exact science and has many potential flaws. One man was imprisoned for six years in Massachusetts for shooting a police officer, only to be released in 2004 when the fingerprint evidence that was used to convict him was trumped by DNA. For a long time the Department of Justice contended that there was a zero error rate in fingerprint analysis. In a study conducted by FBI’s Latent Fingerprint Section in Quantico, Virginia, concluded that the chance to be mistake a fingerprint for someone else was 1 in 1097. This study was conducted on 50,000 pre-existing images and compared electronically against the whole data set, thus producing 2.5 billion comparisons.
However, many advocates against the admissibility of fingerprinting continue to jump on the bandwagon and believe the study does not reflect what happens in life. In life, partial prints from a crime scene can be messy and send an invalid picture of the criminal. In an unpublished study conducted by 92 students that had one year of training where they had to match archive and fake crime scenes. The end result was 2 out of 5861 were incorrect, which produced an error rate of 0.0034% (Coghlan, 2005). Results from proficiency tests published and cited in the Journal of Criminal Law and Criminology (Vol. 93, p. 985), report error rates occur at a 0.8% average, and have been known to be as high as 4.4%.
In 1914, Dr. Edmond Locard established the first rules on the minimum number of minutiae necessary for a positive identification. According to his study, if twelve or more concurring points are present when the fingerprint is clear the identity is “beyond debate” (Unknown, Latent Prints, n.d.). If there are eight to twelve concurring points are present the certainty of the identity will be contingent on five additional points. They are the sharpness of the print, the rarity of its type, the presence of the center of the core and the delta in the exploitable part of the print, the presence of pores, and the perfect and obvious identity regarding the width of papillary ridges and valleys, the direction of the lines and the angular value of the bifurcations. If there were less than eight points present, the fingerprints could not provide a valid and accurate identity. Dr. Locard believed that approximately 40 pores in concurrence could establish individuality (Unknown, Latent Prints, n.d.).
Fingerprint Detection: Current Capabilities
Crime scene investigators use a variety of tools to help solve a case. Latent fingerprint detection and identification is among one of the greatest forensic techniques used. The value of fingerprint evidence is insurmountable. An investigator needs to know how to detect, enhance and record the print that has been left behind not visible to the human eye. Latent prints left behind at the crime scene are the most common type of fingerprint evidence, but they are also the ones that can cause the most problems, mainly because it is there, but not to the unaided eye. Utilizing optical, physical or chemical treatments to develop the print comes with precise judgment. The investigator or crime scene technician must distinguish between porous, non-porous and semi-porous surfaces; water insoluble or water soluble, etc.
Just like anything else, latent fingerprints will start to deteriorate and can lead to the loss of clarity over a specific time because of numerous factors. “Elements of this process include evaporation of volatile components (e.g. moisture), diffusion (e.g. through the substrate for porous surfaces and across the surface for non-porous surfaces), decomposition (e.g. bacterial action, oxidation, chemical breakdown due to heat and light, etc.)” (Lennard, 2007). The rate of dehydration will depend on certain factors like the temperature, humidity, and exposure to sun, air currents and the surface on which the print was left. Exposure to high humidity can result in diffusion of a water soluble print, causing the print to be lost, and any detection techniques to be ineffective.
Using optical detection techniques will aid in finding latent fingerprints. Luminescence will help display a weak friction ridge detail. The best optical detection is achieved by using short-wave ultraviolet (UV) light. This technique is highly effective because the light acts as a contrast between the surface by absorbing the light or reflecting it back showing the presence of print.
Will DNA Replace Fingerprints in the 21st Century?
The use of fingerprints to help solve crimes was first suggested by Dr.
Henry Faulds in 1880. Twelve years later, fingerprints that were left in blood at the scene of a double murder in Argentina were used to convict and identify the killer. However, the first fingerprints accepted in court in the United States didn’t happen until 1911.
When we are born, we have distinct patterns on the tips of our fingers that will only change under a biological variation, because once formed in womb, the ridges are permanent and unique to each individual. “Biological variation is also known as the natural law of variation and is sometimes stated as ‘Nature never repeats’” (Leo, 2005). There are three basic types of fingerprint patterns: loops, whorls, and arches. Each of these patterns are arranged to give individuals unique ridges that make up the person’s characteristics of fingerprints.
It is when these ridges are examined under a microscope side by side with a known source that a person can be confirmed or eliminated as a suspect. With new technology, fingerprint evidence can be searched through automated fingerprint information systems (AFIS). Fingerprints are used to establish a person’s identity in the United States and in every other country in the world. Fingerprints are not just used as evidence in a crime (criminal history), but for employment and security clearances.
Deoxyribonucleic acid (DNA) was discovered in 1911. It was also discovered that this DNA was the carrier of genetic information. However, it wasn’t until 1985 that the structure also established the uniqueness of each person. One year later, the first use of DNA in a criminal case was used to match a suspect to a double murder in England. The first case of DNA evidence admitted in a United States court didn’t happen until 1988. Since then, over thirty-five states have admitted DNA evidence in one form or another while more than twenty-five states have the population frequency data or statistics to be admissible in court (Leo, 2005).
DNA evidence is found at crime scenes as the presence of blood, semen, hair, skin, and saliva. In order to make a comparison a DNA profile must be extracted from the evidence and/or a sample taken from a known individual. A DNA profile is accomplished through a process called electrophoresis.
After the profile has been extracted, the results are recorded on an autorad and can be compared to other profiles. There are thirteen markers that are used to standardize a national data base called Combined DNA Index System (CODIS) in the United States (Leo, 2005). To date, DNA is still emerging as we continue to move further into the technological future, and can be used for personal identification, employment, security clearance, or to track criminal histories.
Every second of the day, millions of fingerprints are being searched via the automated fingerprint systems around the world. Thousands of crimes have been solved because of the fingerprint evidence left behind at the scene of the crime. In 1994, when CODIS began, there have been over 20,000 DNA matches. In Los Angeles County, California, more than 500 latent prints are matched to criminal offender on any given day (Leo, 2005). Both methods of identifying an individual play crucial roles in solving crime. Although fingerprints are still considered the “golden standard” for forensic evidence in the courtroom (Leo, 2005), DNA is moving forward in being a very important tool to combat and solve crime. However, when it comes down to it, both techniques complement each other and provide vital information to help find criminals.
Coghlan, A. &. (2005). How Far Should Prints be Trusted? New Scientist, 2517(187), 6-7. Retrieved January 21, 2013, from http://search.ebscohost.com.proxy.devry.edu/login.aspx?direct=true&db=a9h&an=18376323&site=ehost-live Lennard, C. (2007, December). Fingerprint Detection: Current Capabilities. Australian Journal of Forensic Science, 39(2), 55-59. Retrieved January 21, 2013, from http://www.informaworld.com Leo, W. (2005, September/October). Will DNA Replace Fingerprints in the 21st Century. The Print, 21(5), 1-5. Retrieved January 21, 2013, from http://www.fingerprintidentification.net/sitebuildercontent/sitebuilderfiles/dnavfingerprints.pdf Spraggs, D. (2007, February 01). How to Lift Fingerprints. Retrieved January 20, 2013, from Police Magazine: www.policemag.com/channel/patrol/articles/2007/02/how-to-lift-fingerprints.as
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