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Monday, July 15, 2013

Processing the Crime Scene



     Upon the discovery of the deceased female in her bedroom and determining that she had been a victim of rape, it is up to the forensic investigator to process the scene and determine what kind of evidence has been left behind so to attempt to identify the perpetrator .  By collecting physical evidence, possible suspects can be identified or eliminated and can help to either corroborate or dispute their statements.  Most often, the evidence found in a sexual assault case would include biological evidence such as semen, blood, and skin cells along with hair, fibers and other trace evidence, and impression evidence such as fingerprints, shoeprints or tool marks.


     When arriving at the crime scene, all items with possible evidentiary value should be collected. Information about what had occurred should be obtained and then the crime scene should be processed in a systematic manner for evidence:
     • Bedding - Collect the bedding that the assault occurred upon. If wet stains are located, their location should be shown by using a piece of tape while they are allowed to air dry.  Once dry, they should be packaged in a paper bag, folded with the edges toward the center.
     • Biological Evidence - This type evidence includes hair, blood, semen, saliva, and other body fluid secretions. A control sample should be taken from an unstained area of material near the collected stain using a clean, dry cotton swab.  Any evidence found, no matter how small, should be collected.  If needed, a separate forensic light source may help locate any other biological stains that may be present.  An example of a forensic light would be a Polilight or Woods lamp. (Vandenberg, 2006)
       Use tweezers with smooth, easy-to-clean working surfaces to collect the samples.  Should the tweezers become contaminated during the collection process, thoroughly rinse them using a stream of distilled water and dry thoroughly using paper tissue. Before using the tweezers to manipulate another sample, be sure to repeat this process twice. (Spear, pg. 7)
     • Photographs need to be taken in order to identify evidence and record the scene. 
     • A sketch artist will draw the scene in their sketchbook in order to establish spatial relationships.
     • Fingerprints are the best way of identification of the suspect(s). Fingerprint collection should be done on anything that the perpetrator may have touched.  The fingerprints may be visible, making identification simple; or they may be hidden, meaning dusting and/or other chemical means may be necessary to raise the prints.
     • If there are any shoeprints, tool-marks, or vehicle tread marks present, an impression may be taken and entered into evidence.  They could then be used to link a possible suspect(s) to the crime.
     • Any other physical evidence that may be present could also have evidentiary value and needs to be collected.  This includes anything that the suspect(s) may have brought with him or had on him.   Collect any evidence that could have possibly come from the victim such as clothing.  Also collect fibers, fingernails, hairs, saliva stains, lubricants or foreign objects used in the assault or discarded clothing.
     The semen stained clothing and bedding should be carefully collected and stored to ensure the preservation for positive analysis at the lab.  Before collection however, safety precautions need to be used to ensure the safety of personnel.  This is due to the fact that all biological evidence can contain infectious organisms such as the AIDS or Hepatitis viruses.
 
    I. The steps to take to ensure safety when handling this type of evidence include:
·          Disposable gloves should be worn at all time
·         Hands or other contaminated items should be kept away from the face to prevent contact with the eyes or nose.
·         Properly dispose of gloves and wash hands with special germicidal soap following the handling of contaminated surfaces.
            When collecting the semen samples from the bedding and clothing, there are certain steps to be taken.  First, be sure to collect as much sample as possible from each source. Do not spread the stain over a large area (i.e.  You need to keep the stain concentrated).  Make sure that you handle the stain in a way that does not deteriorate the sample.   Air-dry the samples as quickly as possible and place them separately in paper bags.  This will ensure that air constantly circulates through them and prevents mold and mildew from forming (Saferstein, 2011).
            You will need to make sure that you do not accidentally mix the biological samples together.  This would cause your samples to become contaminated and unusable.  By placing the samples into separate paper bags, this will be avoided.    Should you get any of the samples on your gloves, you will need to dispose of them and put on a fresh pair.  Finally, you should never talk over any of the evidence samples.  This could cause your DNA to be present due to saliva (spit) and render it unusable.  One way to avoid this would be to wear a face mask.

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  Resources 
  Saferstein, R. (2011). Criminalistics: An introduction to forensic science (10th ed.). Upper Saddle River, NJ: Pearson/Prentice Hall.
  Spear, Theresa. Sample Handling Considerations for Biological Evidence and DNA Extracts. California Criminalistics Institute. 7-8.
  Vandenberg, N., & van Oorschot, R. (2006). The use of Polilight in the detection of seminal fluid, saliva, and bloodstains and comparison with conventional chemical-based screening tests. Journal Of Forensic Sciences, 51(2), 361-370.