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Chapter 9

Blood and Physiological Fluid Evidence: Evaluation and Initial Examination

  • How Biological Evidence Analysis Has Changed Because of DNA Typing
  • Nature of Blood
  • Collection, Preservation, and Packaging of Biological Evidence
  • Test Controls, Substratum Comparison Specimens, and Contamination Issues
  • Initial Examination of and for Biological Evidence
  • Forensic Identification of Blood
  • Species Determination
  • Forensic Identification of Body Fluids
  • Forensic Investigation of Sexual Assault Cases
  • Blood and Body Fluid Individuality: Traditional Approaches

I. How Biological Evidence Analysis has Changed Because of DNA Typing

  • Prior to the introduction of forensic DNA typing analysis, blood groups were the genetic markers that were analyzed from biological evidence (forensic serology)
  • Forensic biology now refers to the preliminary examination of biological evidence prior to the DNA typing analysis procedures

II. Nature of Blood

  • Blood contains cells, nutrients, chemical messengers, and ingested substances
  • A tube of whole blood will clot producing two fractions: a yellow serum layer and a dark red clot containing cellular
    material
  • Anticoagulants prevent
    blood clotting yielding a
    yellow plasma layer and a
    cell fraction that settles to
    the bottom of the tube

II. Nature of Blood

  • The cellular fraction of blood contains red blood cells (erythrocytes) and white blood cells (leucocytes)
  • White blood cells are the
    source of DNA for DNA
    typing analysis
  • Red blood cells do not
    contain any nuclear DNA

III. Collection, Preservation, and Packaging of Biological Evidence

  • Blood or Buccal Swabs from Known Person:
  • Blood is drawn into a vacutainer tube containing an anticoagulant such as EDTA (“purple top” tube)
  • Buccal (cheek) swabs are
    often used in place of liquid
    blood as the known sample

III. Collection, Preservation, and Packaging of Biological Evidence

Biological Evidence from Scenes:

  • Fresh or web blood should be collected on clean, sterile, gauze and allowed to dry
  • Four sampling methods for dried blood:
  • Cutting – For stains on objects that are difficult to submit to the lab. The cut portion should include unstained areas around the bloodstain
  • Swabbing – Stain is transferred to a swab which has been moistened with sterile water or saline.
  • Scraping – a sharp instrument is used to scrape the stain off of a surface & onto clean paper
  • Elution – using a small amount of saline or distilled water to dissolve the dried stain

III. Collection, Preservation, and Packaging of Biological Evidence

  • The most important consideration for preserving biological evidence from scenes is to thoroughly dry the item before packaging and then store in a cool dry environment
  • Biological evidence must be packaged in paper containers that can breathe

IV. Test Controls, Substratum Comparison Specimens, and Contamination Issues

1. Known (Exemplar or Reference) Control:

  • are specimens from a known source
  • essential for comparison with DNA profiles from evidentiary specimens

2. Alibi (Alternative) Known Control:

  • From a known source that may be the source of the evidence

3. Blank Control:

  • A specimen known to be free of the item or substance being tested

IV. Test Controls, Substratum Comparison Specimens, and Contamination Issues

4. Substratum Comparison Specimens:

  • Substratum refers to the underlying material or surface on which the evidence is found
  • A substratum comparison specimen is subjected to the same testing as the evidence
  • The specimen helps to detect interference in lab tests originating from the evidence surface
  • An unstained portion of the evidence underlying material is collected for this purpose

IV. Test Controls, Substratum Comparison Specimens, and Contamination Issues

  • Evidence may be contaminated in several ways:
  • Biological material may have been on a surface before the biological evidence was deposited
  • During scene searching &/or processing activities
  • During laboratory examinations &/or manipulations

V. Initial Examination of and for Biological Evidence

  • The initial examination is designed to evaluate stains for possible evidentiary value
  • Activities include:
  • Searching for biological stains
  • Preliminary tests for physiological fluids
  • Positive preliminary tests are then subjected to confirmatory tests
  • Cutting out or transferring stains to swabs for subsequent examinations

VI. Forensic Identification of Blood

Two categories of identification tests:

  • Presumptive or preliminary test
  • Used for screening specimens that might contain the substance or material of interest
  • Both false positive and false negative results may be obtained
  • Confirmatory test
  • Are tests which are entirely specific for the substance or material for which it is intended
  • A positive confirmatory test is interpreted as an unequivocal demonstration that the specimen contains the substance or material

VI. Forensic Identification of Blood

Presumptive Tests for Blood:

  • Presumptive blood tests are used to screen evidence for the possible presence of blood
  • Most are color tests and are based on the peroxidase-like activity of hemoglobin
  • Peroxidase catalyzes the following reaction
  • Reduced Dye + peroxide --> Oxidized dye + water
  • The presence of hemoglobin catalyzes the reaction, forming a colored dye product
  • Positive presumptive tests do not prove that blood is present

VI. Forensic Identification of Blood

Confirmatory Tests for Blood:

  • Older tests included crystal tests such as the Teichmann and Takayama tests
  • Current immunological tests use antibodies specific for human hemoglobin, thus combining the confirmatory test for blood with a human species test
  • The crystal tests and the immunological tests are known as direct confirmatory tests

VII. Species Determination

  • Tests must be done on blood specimens to determine the species of origin
  • Species origin tests are done using immunological methods which involve the interaction of antigens and antibodies
  • Hemoglobin from human red blood cells can be used as the antigen to produce anti-human hemoglobin serum
  • Specific antiserum can be used to test for the presence of antigens in unknown specimens

VII. Species Determination

  • Common immunological species tests include the Ouchterlony method
  • Extracts of the bloodstain to be analyzed are tested with specific antisera
  • If the bloodstain contains the antigens corresponding to the specificity of the antiserum, a visible precipitate (precipitin) is obtained

VIII. Forensic Identification of Body Fluids

1. Identification of Semen:

  • Semen is a mixture of specialized cells, called spermatozoa, suspended in a fluid known as seminal plasma
  • UV light causes semen stains to fluoresce, and is therefore used to locate
    stains
  • Both presumptive and
    confirmatory tests for
    semen stains are available

VIII. Forensic Identification of Body Fluids

Presumptive Test for Semen:

  • The AP test is a color test based on the detection of acid phosphatase, an enzyme from the prostate gland that is found in high concentration in human semen

Confirmatory Test for Semen:

  • A commonly used approach is to use a microscope to detect spermatozoa in smears made from dried stains
  • When no sperm are found, immunological methods are used to detect the presence of a prostate gland protein called p30 or PSA

VIII. Forensic Identification of Body Fluids

2. Identification of Vaginal Secretions, Saliva, and Urine:

  • There are no reliable methods for identifying human vaginal material
  • Presumptive tests for saliva are based on the presence of the enzyme amylase
  • There are no confirmatory tests for saliva
  • Presumptive tests for urine are based on the presence of urea and creatinine
  • There are no confirmatory tests for urine

IX. Forensic Investigation of Sexual Assault Cases

1. Coordination of Effort – SANEs and SARTs

  • The medical examination of complainants in sexual assault cases is performed by specially trained sexual assault nurse examiners (SANE)
  • Forensic nurses take a lead role in the coordinated response by the sexual assault response team (SART)
  • Complainants are taken to a medical facilities or a SANE/SART facility to attend to their medical needs and to collect relevant evidence using a sexual assault evidence collection kit (”rape kit”)

IX. Forensic Investigation of Sexual Assault Cases

2. The Forensic Scientist’s Role:

  • Sexual assault evidence collection kits are forwarded to the forensic lab for examination
  • The forensic scientist’s primary role is the analysis of the physical evidence
  • If semen is present it helps to establish the corpus delicti
  • If semen or other fluids are found, DNA typing is conducted to determine if there is a match to a suspect or an exclusion

IX. Forensic Investigation of Sexual Assault Cases

3. Medical Examination:

  • Medical evaluation and treatment of sexual assault victims initially involves recording the history of the events, tending to any injuries, and documenting any injuries, bruises, or contusions
  • This is followed by evidence collection, which includes clothing, vaginal swabs, pubic hair combings, any stains on the skin surface, and a known control (blood or buccal swab)

IX. Forensic Investigation of Sexual Assault Cases

4. Sexual Assault Evidence Collection Kits:

  • Sexual assault evidence collection kits contain a variety of containers and envelopes plus a detailed set of instructions on how to use them
  • Not every container/envelope is used in every case

IX. Forensic Investigation of Sexual Assault Cases

5. Types of Sexual Assault Cases

  • There are three types of sexual assault cases: unknown offender (identification cases), known offender (consent cases), and sexual assaults involving children
  • DNA profiling is helpful in identification cases but not in consent cases
  • State laws define the age of consent, thereby differentiating between an adult and child

IX. Forensic Investigation of Sexual Assault Cases

6. Drug Facilitated Sexual Assault:

  • Several drugs are commonly encountered as “date rape” drugs: rohypnol, GHB, & ketamine
  • All are depressants with amnestic effects, and are often used along with alcohol
  • These types of cases require toxicological analysis of the evidence

X. Blood and Body Fluid Individuality: Traditional Approaches

1. The Classical or Conventional Genetic Markers:

  • 5 categories of classical genetic markers: blood groups, isoenzymes, plasma (serum) proteins, hemoglobin variants, and HLA
  • The first blood group markers were ABO, discovered in 1901 by Karl Landsteiner

X. Blood and Body Fluid Individuality: Traditional Approaches

  • ABO markers were first applied to criminal cases involving bloodstains by Dr. Leon Lattes of Italy in 1913
  • Isoenzymes are enzymes which occur in multiple molecular forms, reflecting differences in the gene that code for the enzyme
  • Similarly, there are common variants of the protein hemoglobin

X. Blood and Body Fluid Individuality: Traditional Approaches

2. How Does Typing Genetic Markers Help “Individualize” a Biological Specimen?

  • A gene is a region of DNA that codes for a particular protein or enzyme
  • Because chromosomes are paired (maternal and paternal), and there is one gene on each chromosome, the genes are paired
  • A gene locus is the location on a chromosome where a particular trait is determined

X. Blood and Body Fluid Individuality: Traditional Approaches

  • The genes making up a pair at a given locus are called alleles
  • The alleles may be the same (homozygous) or different (heterozygous)
  • Population genetics looks at how often alleles found at a given locus occur in a population
  • A portion of a large population is sampled and tested to determine the frequency of a particular allele
  • Statistics are used to estimate the frequency of an allele in the entire population