452 lines
24 KiB
Plaintext
452 lines
24 KiB
Plaintext
October 1990
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SEROLOGICAL EVIDENCE
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IN SEXUAL ASSAULT INVESTIGATIONS
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By
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Robert R.J. Grispino, M.A.
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Special Agent
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Serology Unit, Laboratory Division
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FBI Headquarters
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NOTE: The following article presents a purely scientific
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approach to sexual assault evidence collection. The
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scientific step-by-step procedures that are explained here
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should always be accompanied by supportive treatment of the
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victim. It should also be noted that the investigating
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officer will be responsible for both overseeing the
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execution of the medical procedures described and managing
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the collection of the physical evidence.
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Police officers throughout the United States routinely
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handle and oversee sexual assault investigations. Yet, these
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officers rarely receive training on the proper methods to be used
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for sexual assault evidence collection and preservation. As a
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result, valuable physical evidence may either be overlooked or
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inadvertently allowed to deteriorate biologically. This article
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establishes proper evidence collection and preservation protocol
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in sexual assault matters and demonstrates how modern forensic
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serology can aid in the eventual successful prosecution of the
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assailant.
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AFTER THE ASSAULT
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A sexual assault has been committed. Upon arriving at the
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scene, an officer usually encounters a distraught, possibly
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hysterical, victim in the first psychological coping stages
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after an intrusively brutal assault. At this time, the victim
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is not usually receptive to examination, even though the ideal
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time to collect body fluid evidence is immediately following the
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assault. This best evidence of the crime is present, but
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unfortunately, it is degrading with every elapsed minute. It is
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crucial that the officer be aware of the need for immediate
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examination in order to ensure that evidence is collected
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properly.
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The victim should be transported expeditiously to a local
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hospital or rape trauma center where trained nurses or
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physicians can gather the appropriate physical evidence. The
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investigating officer is not only responsible for accompanying
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the victim through the phases of the examination but must also
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oversee the collection and preservation of medical evidence. By
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being fully aware of the procedures that should take place and
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the evidence that can be collected, the officer will be able to
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ensure that the case is as complete as possible.
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During this examination period, health professionals should
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accumulate and catalog physical evidence. The completeness of
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the physical examination depends on the care, consideration, and
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thoroughness of the examining physician. As much evidence as
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possible should be obtained from the victim. However, if the
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health professional does not gather all of the available
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background data, the investigating officer can and should step in
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to make sure that it is elicited entirely from the victim.
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INTERVIEWING THE VICTIM
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The initial victim interview is notoriously the most
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incomplete in sexual assault matters. The excuses are numerous.
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The victim is hysterical and has to be sedated. The doctor or
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nurse is not willing to delve into any particulars of the assault
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for fear that it will further upset the victim. The
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investigating officer is embarrassed or unsure of the situation.
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Yet, regardless of these various problems, a full and complete
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description of the assault is crucial to obtain the physical
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evidence needed for a successful scientific analysis.
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Obvious questions regarding the date, time and location of
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the assault, as well as the description or identity of the
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subject and the general circumstances of the assault, are rarely
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missed. However, the less obvious questions can be just as
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important. The interviewer should ascertain whether the victim
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bathed, showered, douched, urinated, defecated, vomited, brushed
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teeth, or gargled with mouthwash at any time after the assault
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and prior to the examination. If any of these activities were
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performed, the probability of obtaining useful serological
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results could be greatly diminished.
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The physician should then discuss the basics of the assault.
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It should be determined from the interview whether penile
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penetration of the vagina, anus or mouth was attempted and/or
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successful, as well as if the perpetrator ejaculated at any time.
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If penetration was unsuccessful or not attempted in certain
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orifices, the physician may opt not to collect evidence from the
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unviolated areas. The physician must realize that it may be
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difficult or impossible for a victim to know whether the suspect
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ejaculated or there may be a psychologically induced reluctance
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by the victim to admit during the early post-assault period that
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ejaculation occurred. In these instances, failure to collect
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samples from all body cavities may result in lost body fluid
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evidence.
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The extent of oral/genital sexual contact, whether fellatio
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or cunnilingus, should be evaluated. If contact was indicated,
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the medical examiner should externally swab the genital area for
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later serological analysis. It would also be important to
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determine whether the assailant used a lubricant or condom during
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the assault or whether the victim was menstruating.
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The victim should also be asked about the particulars and
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extent of any consensual intercourse within a 72-hour period
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prior to the assault. The final serological conclusions reached
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from the scientific analysis of the physical evidence of the
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assault may be greatly affected by previous consensual sexual
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activity and resultant body fluid mixtures. It would then be
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important to obtain blood and saliva samples from the previous
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partner(s) for comparison and elimination purposes.
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The presence and extent of any injuries to the assailant
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inflicted by the victim is also extremely important. The suspect
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may have bled on the victim from a victim-inflicted injury during
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the struggle. A victim during menstruation could also transfer
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blood to the suspect during vaginal assault, which could be
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serologically identified in the suspect's underwear.
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After all background information is obtained from the
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victim, the staff nurse and attending physician should conduct a
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thorough pelvic examination of the victim. All signs of pelvic
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injury should be documented, either in drawing or photographic
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form. After the background information has been gathered, the
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next step is to collect physical evidence from the victim as
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carefully and thoroughly as possible.
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COLLECTING PHYSICAL EVIDENCE
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Many of the items used for evidence collection are available
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in sexual assault kits. However, these commercial kits vary
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widely, and basic minimums should be considered.
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Vaginal, oral and/or anal swabs should be taken from the
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victim using sterile cotton swabs. These swabs should then be
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air-dried, appropriately labeled, initialed by the examiner and
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packaged separately. In most assaults involving vaginal
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penetration, two to four vaginal swabs and two cervical swabs are
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adequate for analysis. In cases of oral or anal sodomy, oral or
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anal swabs should be obtained from the victim. Two clean swabs
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taken from the same package as the unstained control swabs should
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be submitted to show that any useful serology results obtained
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during analysis were due to body fluids and not any contaminant
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initially on the swabs.
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Smear slides, unfixed and unstained, are sometimes useful
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for demonstrating the presence of sperm cells (spermatozoa).
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Vaginal, oral and/or anal smear slides should be obtained from
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the victim using the same swabs mentioned above. The smear
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slides should be appropriately labeled and should indicate which
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individual swab was used to create which microscope smear slide.
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Examining physicians in some jurisdictions prepare and
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microscopically examine smear slides to determine the presence of
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motile sperm cells indicative of recent sexual activity. In such
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cases, examining physicians may be required to testify in court
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proceedings regarding their observations. In any event, stained
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and fixed smear slides are useless for further serological
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analysis and should not be submitted to crime laboratories.
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Pubic combings should be taken from the victim to identify
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any foreign hairs or fibers that may have been transferred during
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the assault. The physician should comb the pubic area and submit
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the comb and any resultant debris in an appropriately marked,
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sealed envelope. Head hair combings should be obtained from the
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victim in cases where other evidence is insufficient to show
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interpersonal contact. Pubic and head hair combings should also
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be obtained from the suspect if appropriate to the investigation.
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Any obvious debris (soil, fibers, hair, grass, etc.)
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observed during the examination of the victim should be collected
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and submitted in a separate envelope describing the location of
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the debris. The examining physician should also scrape all
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residue from under the fingernails of each hand of the victim and
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place the residue in a specimen envelope or clip the fingernails
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and place the clippings in separately labeled envelopes.
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Using a sterile pad that has been moistened lightly with
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distilled water, the physician should swab the vulva and the
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inner portion of the victim's thighs adjacent to the vaginal
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area. The genital swabbing pad should then be air-dried and
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submitted for laboratory analysis in an appropriately labeled
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specimen envelope.
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The physician should swab any dried secretions observed
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during the examination of the victim, i.e., saliva around bite
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marks, using a sterile pad that has been moistened lightly with
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distilled water. The pad should also be air-dried and submitted
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for analysis. In cases where dried blood or encrusted semen is
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observed, the material should be scraped from the body into a
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specimen envelope and submitted for analysis. Encrusted matter
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should never be re-hydrated, since it dilutes the sample. The
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location of each sample should be noted on a body diagram. Pubic
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or head hair containing encrusted semen should be carefully
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clipped and placed in a labeled specimen envelope.
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In the event of oral ejaculation, gagging, swallowing or
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regurgitation during the assault may force air carrying semen
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through the nasal passages. The victim should blow her nose,
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very hard, several times into the center of filter paper. The
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resultant nasal mucous sample should be allowed to air dry and
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then submitted for analysis.
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STANDARDS
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Head hair and pubic hair standard samples should be obtained
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from the victim and any suspects developed from the sexual
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assault investigation. The hair samples should be pulled with
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the bulb intact, not clipped. Head hair samples should be taken
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from four separate areas of the scalp. Twenty-five full-length
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hairs are generally considered adequate to represent an
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individual's hair characteristics.
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Liquid blood samples should also be obtained from the
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victim, any consensual sexual partners from at least 72 hours
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prior to the assault, and any developed suspects. Known blood
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and saliva samples from a suspect in a sexual assault case must
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usually be obtained through a court order issued by a judge or
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local magistrate. Blood samples from each individual should be
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collected in both red-topped and purple-topped blood collection
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tubes. Red-topped tubes are used for traditional serological
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analysis, such as ABO grouping, secretor status and enzyme
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electrophoresis. A red-topped tube indicates that the collected
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blood is exposed to no preservatives or blood anticoagulants.
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Purple-topped tubes are used for DNA profiling only. These tubes
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contain a chemical chelator (EDTA) that inhibits the action of
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enzymes that would normally act to break down the DNA molecules
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in the blood samples. In the event that toxicology examinations
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will be requested, an additional blood sample taken in a
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grey-topped tube (containing sodium fluoride) and a 10 cc. urine
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sample should also be collected. All of the collected blood and
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urine should be refrigerated, not frozen, and submitted for
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analysis as soon as possible.
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Dried saliva samples should also be obtained from the
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victim, from consensual sexual partners from at least 72 hours
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prior to the assault, and from any developed suspects. The donor
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should expectorate on filter paper to produce a stain
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approximately 1 1/2 inches in diameter. Saliva should be clean
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and undiluted. Prior to giving the sample, the donor must have
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abstained from eating (food, gum, chewing tobacco), drinking and
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smoking for about 30 minutes. The stain should be circled in
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pencil before the drying is complete. When the samples have
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air-dried completely, they should be placed in a specimen
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envelope that has been dated and initialed.
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MISCELLANEOUS SAMPLES
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The officer should make sure that the clothing worn by the
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victim during the sexual assault is collected. The victim should
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always disrobe over examination paper. The victim's panties,
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pantyhose, jeans, shirt, shoes, socks, dress, or nightgown should
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be separated and individually packaged as appropriate. Any
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physical evidence from the crime scene that may bear suspected
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semen stains, such as bed sheets, towels, wash cloths, paper
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towels, toilet paper or tissue paper, should also be collected.
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The examination paper should also be submitted for analysis in
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the event that hair or fiber mixtures from the assault fell from
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the victim while disrobing.
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The collected items should be clearly described for the
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laboratory, including whether the items came in contact with the
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victim and/or suspect before, during, and/or after the assault.
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Stained areas believed to exhibit evidence of the assault should
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be described or highlighted. For example, only a small area on a
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bedsheet may be relevant to the investigation. Therefore,
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forensic examination of the entire bedsheet for semen may not
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only be unnecessary and wasteful of forensic services but may
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also dilute the effectiveness of the examination.
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PRESERVATION AND PACKAGING
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Bacteria begin to degrade biological fluids immediately
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after deposition. They especially thrive on the rich nutrients
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present in semen. If unchecked, contaminant bacteria can
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completely destroy DNA and other genetic markers of value. To
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counteract this phenomenon in all of the above instances in
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which moist body fluids are collected, it is imperative that the
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samples be completely dried. After drying, the specimen(s)
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should be placed into breathable paper bags or envelopes and
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frozen or refrigerated until submitted to the laboratory for
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analysis.
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All collected items of evidence should be properly
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catalogued with preserved chain-of-custody records for court
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presentation purposes. All items should be dated and initialed
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by the collector. In cases where samples were taken by health
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professionals, they should identify, date and initial the items
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and hand the evidence to the investigating officer. Whenever
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possible, collection of known blood, urine and saliva samples
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should be performed under the supervision of the investigating
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police officer.
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CONCLUSION
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Each sexual assault occurs under circumstances unique to the
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victim, the crime scene, and the suspect. If extensive
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information is provided to the examiner in the crime laboratory,
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the examiner can conduct a more thorough and complete scientific
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analysis. Probative value and relevance to the investigation are
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the watchwords in collecting and preserving the evidence of a
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sexual assault. If collected materials are stored in plastic
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bags under room temperature for any extent of time, the
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biodegrading action of contaminant bacteria may jeopardize
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conclusive test results. Sexual assault evidence kits with all
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of the above-mentioned materials are commercially available and
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stocked by hospitals and rape crisis centers.
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Proper collection, identification, packaging and storing of
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evidence in sexual assault investigations will greatly improve
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the chances for a successful prosecution of the perpetrator, as
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long as the investigating officer follows up with good
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communication and contact with the laboratory examiner in all
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stages of the case. The evidence sent to the forensic laboratory
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should be accompanied by a transmittal letter that completely
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describes the facts of the crime, the inventory of the evidence
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seized, and the scientific examinations requested. It is
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suggested that the report of the initial examining physician be
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included along with the evidence.
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Criminal investigators and prosecutors must familiarize
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themselves with proper procedures concerning the collection,
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identification, and packaging of serological evidence, as well as
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to establish effective communication with the examiner. By doing
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this, and by understanding the practical capabilities and
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limitations of modern forensic serology, the interests of justice
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can be best served with a successful prosecution of the
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perpetrator in a sexual assault.
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APPENDIX A:
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THE ROLE OF SEROLOGY
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Forensic serology is best defined as the science involving
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the identification and characterization of blood, semen, and
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other body fluids, usually found in dried stain form on items of
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physical evidence. Because of its supportive nature to the
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prosecution, it is absolutely essential that the investigators
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and the prosecutor understand, at least in general terms, the
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capabilities, as well as the limitations, of forensic serology.
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Under most conventional serology protocols, items of
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physical evidence in sexual assault cases are sceintifically
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screened for the presence of human semen and blood. Semen is
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identified where sperm cells are microscopically identified
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and/or a semen-specific protein associated with human semen,
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known as p30 or prostatic antigen, is determined to be present
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in extracts of dried stains under examination.
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Once the presence of semen is established, the stain
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extracts may be analyzed for the presence or absence of blood
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group substances. Eighty percent of the general population
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secrete chemicals (blood group substances) into their body
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fluids that are consistent with their red blood cell ABO type.
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In these people, known as secretors, analysis of their saliva,
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vaginal secretions, or semen will indicate whether they belong
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to blood group A, B, AB or O.
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If human blood is identified on an item, attempts may be
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made to determine whether the blood is of A, B, AB or O. Then,
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depending upon the size of the dried stain, it may be analyzed
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using electrophoresis to determine as many genetic marker
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protein types as possible. In order for any of this to make
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sense, known blood and saliva samples from both the victim and
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suspect of the sexual assault must be submitted for analysis and
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comparison purposes.
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The known blood samples may be grouped as to A-B-O blood
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type and assorted genetic enzyme markers. The serologist may
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also attempt to determine if the individual is a secretor from
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analysis of the liquid blood and/or dried saliva standard.
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Once all of the scientific information is assembled, the
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serology examiner may be able to make expert conclusions from
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the findings. Forensic serology is a comparison science. If
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all of the information from the analysis of the questioned
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samples is identical to that obtained from the known blood and
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saliva samples from the suspect, then the serologist can
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conclude that the suspect was a possible source of the deposited
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semen or blood stain. If, however, one element of the profile
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differs, then the serologist may be able to absolutely exclude
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the suspect as a source of that body fluid. It is further
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emphasized that without known standards from the victim,
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suspect(s) and any other involved parties for comparison, the
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effective serological analysis of items of evidence from the
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assault may be rendered meaningless.
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Using this technology, the best that a serologist may be
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able to say is that the suspect is a possible depositor of the
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body fluid. This is because other potential suspects in the
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general population may share the same A-B-O blood type, secretor
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status, and enzyme profile, althought the implementation of DNA
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testing in forensic samples has dramatically altered this
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thinking.
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APPENDIX B:
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DNA PROFILING
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Deoxyribonucleic acid (DNA) is an organic substance found
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primarily in the chromosomes within the nuclei of cells. Using
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electrophoresis and radioactive probing techniques, a DNA
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profile can be developed from dried blood and semen stains.
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DNA profiling is the FBI Laboratory's primary method of
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choice for the serological analysis of physical evidence from
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violent personal crimes. This technology has revolutionized the
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processing of serological evidence and has superceded
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traditional serology techniques in its associative value.
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Currently, the FBI Laboratory screens probative items of
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evidence in sexual assault matters, such as vaginal, oral, and
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anal swabs and panties from the victim, for the presence of
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semen. At the conclusion of this analysis, the remaining stain
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may be submitted for DNA profiling. If human semen is
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identified, the sample is submitted for DNA analysis.
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DNA profiles in the questioned samples are compared side by
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side with the DNA profiles in the known blood samples from the
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victim and suspect. If the patterns on the suspect's blood
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profile match those generated from the questioned samples, the
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serologist can testify that the semen or blood was deposited by
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the suspect or a member of a group of individuals who share this
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profile. As with conventional serology, if DNA profiles do not
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match, the serologist can absolutely exclude the suspect as the
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contributor of that DNA sample.
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Many U.S. crime laboratories do not possess the capability
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to conduct DNA testing. Therefore, investigators and
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prosecutors should become familiar with the capabilities of
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their local laboratories in this regard. The current protocol
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used at the FBI Laboratory necessitates an 8- to 10-week time
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period from initial DNA extraction to final probing results in
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each case sample. Additonal delays may also exist due to high
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caseload and the requirement for analysis in other forensic
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disciplines. DNA analysis may be more time-consuming and labor
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intensive than traditional serology techniques; however, the
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results may be far more significant or informative. The law
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enforcement community must be aware that DNA analysis of
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forensic samples is a lenghty process and trial continuances may
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be necessary.
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