Chapter 9. Blood and Physiological Fluid Evidence: Evaluation and Initial Examination How Biological...

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


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


• 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


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


• 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


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


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


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


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”)


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


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)


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


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


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


• 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


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


• 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

Chapter 9. Blood and Physiological Fluid Evidence: Evaluation and Initial Examination How Biological...

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