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Title: PowerPoint Presentation Author: NVRHS Last modified by: Early College User Created Date: 9/18/2005 12:51:39 AM Document presentation format – PowerPoint PPT presentation

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  • Chapter 8

Stain Patterns of Blood
  • The location, distribution, and appearance of
    bloodstains and spatters give useful information
    for reconstructing the events that produced the
  • Surface texture and the stains shape, size, and
    location must be considered when determining the
    direction, dropping distance, and angle of impact
    of a bloodstain.

Stain Patterns of Blood
  • Surface texture is important. The harder and less
    porous the surface, the less spatter.
  • The direction of travel of blood striking an
    object may be determined because the pointed end
    of a bloodstain always faces its direction of its
  • The impact angle of blood on a flat surface can
    be determined by measuring the degree of circular
    distortion. At right angles the blood drop is
    circular, as the angle decreases, the stain
    becomes elongated.
  • The origin of a blood spatter in a
    two-dimensional projection can be established by
    drawing straight lines through the long axis of
    several individual bloodstains. The intersection
    or point of convergence of the lines represents
    the origin point.

Projection of Blood
  • Forensic investigators can determine how
  • blood was projected from the body by
  • examining factors such as
  • Type of injuries
  • The order in which the wounds were received
  • Whose blood is present
  • The type of weapon that caused the injuries
  • Whether the victim was in motion or lying still
    when the injury was inflicted
  • Whether the victim was moved after the injury was
  • How far the blood drops fell before hitting the
    surface where they were found.

Blood Crime SceneCategories of Blood Patterns
  • Pools of blood have evidentiary value in
  • collecting a wet sample. Drops of blood can
  • reveal the height and angle from which the
  • blood fell onto the surface. According to
  • forensic scientists, the blood spatter
  • analysis claims that blood which falls
  • perpendicular to the floor from a distance
  • of zero to two feet would create a circular
  • drop with slightly frayed edges. Drops from
  • a higher distance would have more distinct
  • tendrils extending off the edges.

Blood Crime SceneCategories of Blood Patterns
  • A blood smear on the wall or floor can
  • indicate the direction of force of the
  • blow.  The direction of force is always in the
    direction towards the tail, or smaller end, of
    the smear. In other words, the largest area
  • of the smear is the point of origin. Blood
  • crusts must be tested with crystalline
  • techniques to verify that they are actually
  • blood. Refrigerated red blood cells have a
  • shelf life of about forty-two days, and the
  • serum containing white blood cells can be
  • refrigerated much longer, almost up to a
  • year.  DNA can be extracted from blood (if
  • white blood cells which always contain a
  • nucleus are present), and also from sperm,
  • bone marrow, tooth pulp, and hair roots.

Blood Crime Scene
  • Regardless of what type of analysis is used
  • on the blood at the crime scene, care must
  • be taken to handle it properly and to
  • prevent putrefaction.  Photographs and
  • notes should be taken before any blood is
  • lifted.  Samples should not be exposed to
  • heat, moisture, or bacterial contamination,
  • because these factors can shorten the
  • survival time of proteins, enzymes, and
  • antigens.  Delays in bringing samples to the
  • lab must be avoided at all cost, because it
  • can diminish evidential value.

Court Significance
  • Experts in bloodstain examination are
  • usually law enforcement personnel. In
  • certain jurisdictions, a police investigator
  • or blood specialist may testify on the core
  • issue because blood evidence is usually a
  • vital aspect of the crime scene.
  • An expert in bloodstain examination has
  • Completed specialized training
  • Conducted a sufficient number of
  • examinations
  • Accumulated enough reference patterns
  • to reinforce an argument

Heredity and Paternity
  • The transfer of hereditary material is
    accomplished by means of units called genes,
    located on chromosomes.
  • Alleles Alternative forms of genes that
    influence a given characteristic (such as eye
    color or blood type).
  • Paternity testing has historically involved the
    A-B-O blood typing system, along with blood
    factors such as Rh (D).
  • DNA test procedures raise the odds of
    establishing paternity beyond 99.

Principles of Heredity
  • Transmission of Traits
  • Accomplished by genes, which is the basic unit of
  • Genes are on chromosomes (46 in 23 pairs).
  • The human egg and human sperm contain 23
    chromosomes, which combine during fertilization.
  • A female has XX chromosome, and male has XY
  • Transmission of Traits
  • Genes and chromosomes come in pairs.
  • The position of a gene on the chromosome is
    called the locus.
  • Alleles are alternative forms of genes that
    influence an inherited characteristic.
  • An example of allele genes is the A-B-O blood
    type system.

Principles of Heredity
  • Transmission of Traits
  • A-B-O blood types
  • When a gene is made of two similar genes, they
    are said to be homozygous. Examples include AA or
  • If the gene is made up of two different genes, it
    is said to be heterozygous. An example would be
  • A and B genes are dominant, while O genes are
  • A pair of A-B-O allele genes together are the
    genotype of an individual.
  • The phenotype of an individual is the outward
    characteristic of the individual.
  • There is no lab test to determine a persons
    A-B-O genotype.
  • If the genotypes of both parents are known, a
    Punnet square may be constructed to determine
    potential genotype of offspring.

Blood DNA Testing
  • Blood is used in DNA testing, as shown by
  • the following steps
  • 1. Blood samples are collected from the
  • victim, defendant, and crime scene.
  • 2. White blood cells are separated from red
  • blood cells.
  • 3. DNA is extracted from the nuclei of white
    blood cells.
  • 4. A restrictive enzyme is used to cut
  • fragments of the DNA strand.
  • 5. DNA fragments are put into a bed of gel
  • with electrodes at either end.
  • 6. Electric current sorts DNA fragments by
  • length.
  • 7. An absorbent blotter soaks up the imprint it
  • is radioactively treated, and an X-ray
  • photograph, called an autoradiograph, is
  • produced.

Forensic Characteristics of Semen
  • Normal male can ejaculate 2.5-6 ml of seminal
  • Each ml contains 100 million or more spermatozoa

Testing for Semen
  • Stain must be located and collected
  • Acid Phosphatase Color Test
  • Purple color indicates the presence of semen
  • Spermatozoa Test
  • Semen is diluted with water and dried on filter
  • Microscopic examination looks for spermatozoa

Testing for Seminal Stains
  • Many of the cases sent to a forensic laboratory
    involve sexual offenses, making it necessary to
    examine exhibits for the presence of seminal
  • The best way to locate and at the same time
    characterize a seminal stain is to perform the
    acid phosphatase (an enzyme found in seminal
    fluid) color test.
  • A purple color indicates acid phosphatase enzyme.
  • Semen are identified by either the presence of
    spermatozoa or of p30, a protein unique to
    seminal plasma.
  • Forensic scientists can link seminal material to
    an individual by DNA typing.

Rape Evidence
  • Presence of seminal fluid
  • Physical injuries such as bruising or bleeding
    confirms a violent sexual assault took place
  • Transfer of physical evidenceblood, semen,
    fibers, and hairare usually present

Rape Evidence
  • The rape victim must undergo a medical
    examination as soon as possible after the
  • At that time the appropriate items of physical
    evidence including clothing, hairs, and swabs can
    be collected for subsequent laboratory
  • All outer and undergarments should be carefully
    removed and packaged separately in paper (not
    plastic) bags.
  • Bedding, or any objects upon which the assault
    took place, may also be carefully collected.

An antibodyantigenantibody sandwich or complex
is seen as a colored band. This signifies the
presence of PSA in the extract of a stain and
positively identifies human semen.
PSA testing by electrophoresis.
Collection of Rape Evidence
  • All outer and undergarments are collected and
    packaged separately in paper bags
  • Trace evidence is collected by standing on a
    clean sheet while removing clothing
  • Bedding may be recovered if seminal stains are
  • Medical Examination of the victim

Rape Evidence
  • If a suspect is apprehended within 24 hours of
    the assault, it may be possible to detect the
    victims DNA on the males underwear or on a
    penile swab of the suspect.
  • Items routinely collected from the suspect
    include all clothing, pubic hair, head hair,
    penile swab, and a blood sample or buccal swab
    for DNA typing.
  • The forceful physical contact between victim and
    assailant may result in a transfer of such
    physical evidence of blood, semen, saliva, hairs,
    and fibers.

Medical Examination of Victim
  • Pubic Combings
  • Pubic Reference Samples from victim
  • Vaginal swabs and smear
  • Rectal swabs
  • Oral swabs
  • Head hairs
  • Blood sample
  • Fingernail scrapings
  • All clothing
  • Urine specimen

Medical Examination of Suspect
  • All clothing
  • Pubic hair combings
  • Pulled head and pubic hairs for reference samples
  • Penile swab
  • Blood sample or buccal swab