19.Examination of stain and scene

FORENSIC MEDICINE: EXAMINATION OF STAINS AND SCENE OF CRIME

Forensic Serology

• Definition: Study of human body fluids and stains, focusing on medicolegal significance.

BLOOD STAINS

• Importance: Blood stains at a crime scene provide critical information.

  • Footprints or shoe prints in blood can assist in identifying the assailant.

  • Distribution of blood helps determine the manner of death: suicidal, homicidal, or accidental.

  • Pool of blood indicates incapacity of the victim at that spot.

  • A blood trail suggests the victim was injured at a distance from where the body is found.

  • Stained drag marks imply an unconscious victim or corpse was dragged.

  • Types of Bleeding:

    • Venous bleeding: Slow and steady.

    • Arterial bleeding: Characterized by spurting.

  • Shape of Blood Stains:

    • Vertical drops from < 30 cm appear as round spots.

    • Drops from > 30 cm exhibit prickly edges; the higher the drop, the finer and larger the projections.

    • Drops from > 2 m may form ray-like splashes visible up to 15-20 cm away.

  • Impact Shapes:

    • Oblique impacts produce stains resembling exclamation marks, indicating motion direction.

  • Documentation: Photographs are crucial for the reconstruction of crime scenes.

Types of Blood

• Menstrual Blood: Dark in color, unpleasant odor, does not clot unless mixed with semen.

• Vomited Blood: Appears chocolate colored.

• Haemoptysis: Bright red, frothy blood.

• Rape Cases: Blood may be mixed with semen/pubic hairs.

• Insect Sources: Blood stains from insect bites may show insect body parts under microscope.

CHEMICAL EXAMINATION OF BLOOD STAINS (UQ)

Tests to Identify Blood Stains

1. Catalytic Color Tests:

   • Phenolphthalein Test (Kastle-Meyer):

     • Add phenolphthalein reagent (2g + 20g NaOH + 100ml water) and hydrogen peroxide.

     • Positive result: pink color indicates blood presence.

   • Ortho-toluidine Test:

     • Add ortho-toluidine to stain; a blue color indicates blood.

   • Benzidine Test: (UQ)

     • Add benzidine with glacial acetic acid and hydrogen peroxide; an intense blue indicates blood.

2. Confirmatory Tests (Crystal Tests):

   • Hemin Crystal Test (Teichmann’s Test):

     • Mix sample with NaCl and glacial acetic acid; dark brown rhombic crystals signify blood.

   • Hemochromogen Crystal Test (Takayama Test): (UQ)

     • React stain with Takayama reagent; pink feathery crystals indicate blood.

3. Microscopic Examination:

   • Mammalian blood: biconcave, circular, non-nucleated RBCs.

   • Other species vary: e.g., Camel has oval biconvex RBCs; birds and reptiles have nucleated RBCs.

4. Spectroscopic Examination:

   • Blood sample analyzed in a glass chamber to observe absorption bands indicative of hemoglobin types (oxyhemoglobin, reduced hemoglobin, carboxyhemoglobin, methemoglobin).

PRECIPITIN TEST (UQ)

• Purpose: Identifies whether a stain is from human blood.

  • Antiserum produced from injecting human blood into rabbits; used to test for human blood via precipitation reactions.

  • Techniques:

    • Precipitation Ring: Formed by layering antiserum and diluted extract in a test tube.

    • Agar Gel Diffusion: Band formation indicates human blood when reacted with specific antisera.

    • Agar Gel Electrophoresis: Faster method for observing precipitate formation between stains and antisera.

BLOOD GROUPS (UQ)

• Major Groups: A, B, AB, O based on agglutinogens and agglutinins in erythrocytes.

• ABO Phenotypes and Genotypes: Details potential child blood group inheritance based on parental genotypes.

• Rh Factor: Identifies Rh positive or negative blood types based on agglutination reactions; relevant in transfusion and pregnancy cases.

TESTS FOR BLOOD GROUPS FROM STAINS

1. Mixed Agglutination Technique: Interaction of blood-stained fibers with anti-A and anti-B sera to determine blood group type.

2. Absorption Elution Technique: Reaction at low temperatures to confirm antigen presence, with elution resulting in agglutination outside fibers.

Medicolegal Importance of Blood Group Studies

1. Compare victim's blood with stains at crime scenes.

2. Analyze blood from accident scenes.

3. Assist in paternity/maternity disputes.

4. Blood group analysis in secretions like saliva in secretors can provide additional insights.

Additional Blood Groups

• Minor Groups: MNS, Kell, Duffy, Kidd, Lutheran, Gm, Km systems; stability makes them valuable for forensic analysis.

• Bombay Blood Group: Rare condition missing A, B, H antigens, affecting blood group identification.

• HLA-Typing: Used for paternity tests and organ transplantation due to high accuracy.

ABNORMAL HEMOGLOBINS

• Variations in hemoglobin lead to altered conditions; specific types include HbA (adult), HbF (fetal), and various abnormal types linked to diseases.

• Hemoglobin S: Causes sickle cell disease.

• Hemoglobin D-Punjab: Common in certain populations; linked with beta-thalassemia.

SEMINAL STAINS

• Composition: Semen includes cellular (spermatozoa) and non-cellular compartments.

• Tests for Semen:

  1. Florence Test: Identifies choline iodide in stains.

  2. Barberio’s Test: Checks for spermine in prostatic secretions.

  3. Acid Phosphatase Test:

     • Measures high concentrations in semen, confirming presence.

     • Present in vaginal fluid in lower concentrations.

     • Levels decrease gradually over time in vaginal fluid.

  4. Creatine Phosphokinase (CPK)

     • Spermatozoa have a high concentration of CPK.

     • Normal semen contains between 385 to 14,000 Units of CPK/ml.

     • CPK levels greater than 400 Units are diagnostic

  5. Thin Layer Chromatography

     • Choline and spermine can be identified in liquid semen and dried stains using this method.

  6. Prostatic Specific Antigen (PSA or p30)

     • P30 is a glycoprotein from the prostate gland found in seminal plasma, male urine, and blood.

     • It is not found in female tissues or fluids.

     • Detection methods:

       1. Electrophoresis

       2. Enzyme-linked immunoassay

     • Positive results serve as strong confirmatory evidence.

  7. Microscopic Examination

     • Preparation:

       1. Soak stain in normal saline for 30 minutes.

       2. Centrifuge the extracted fluid.

       3. Examine residue under a microscope using eosin-hematoxylin staining, papanicolau stain, ziehl-neelsen stain.

     • Staining Details:

       • Anterior 2/3 of spermatozoa head: light blue (haematoxylin).

       • Posterior 1/3 of the head and tail: deep red or pink (eosin).

     • Spermatozoa Size:

       • Length: approximately 60 μm.

       • Tail: 40-50 μm.

       • Head: 8-10 μm.

       • Body: 10-12 μm.

     • Detection:

       • Spermatozoa can be tested from vaginal swabs, with various staining methods available.

     • Sperm Motility:

       • Full motility lasts up to 3 hours post-ejaculation.

       • 50% motile for up to 8 hours.

       • 10% motile for up to 24 hours.

       • Motile sperm can be detected up to 12 hours post-intercourse; non-motile up to 26 hours (rarely 2-3 days).

       • Heads can be detected from vaginal fluid for up to 9 days and up to 12 days in the cervix and uterus.

       • Structure of spermatozoa (UQ)

         

Saliva Analysis

• Saliva is a thin, clear fluid produced by salivary glands.

• Contains:

  • Ptyalin

  • Amylase

  • Proteins

  • Lipids

  • Inorganic salts

• Amylase Test: Mix saliva extract with starch solution and iodine to observe the reaction; blue discoloration indicates amylase presence.

• Other tests include Barr bodies and DNA analysis from buccal epithelial cells.

Vaginal Fluid Analysis

• Contains:

  • Squamous epithelial cells

  • Acid phosphatase

  • Blood group substances

  • Endometrial cells

  • Glycogen

  • Doderlein bacilli

• DNA Analysis: Conducted on vaginal epithelial cells, especially from penile washes in rape cases.

Urine Analysis

• Components:

  • Urea

  • Uric acid

  • Creatinine

• Blood grouping possible for secretors; DNA analysis feasible with cellular material.

Fecal Stains

• Contains undigested muscle and vegetable fibers; can be tested for stercobilin.

Locard’s Principle of Exchange (UQ)

• Definition: Contact between two objects leads to material exchange.

• Application Examples:

  • In rape cases: Semen, blood, pubic hair on victim and rapist.

  • In murder cases: Victim's blood on weapons or assailants.

  • Marks of bullet gives idea about weapon.

  • For traffic accidents: Evidence like hair or blood on vehicles.

• Trace evidence like blood, fingerprints, and footprints serves as silent evidence that can corroborate or contradict testimonies.

Examination of Scene of Crime

Key Considerations

• Contamination prevention is crucial; early isolation of crime scene is essential.

• Establish a single pathway marked to control access to the corpse.

• Crime Scene Types:

  • Primary Scene: The original location of the crime.

  • Secondary Scene: Location where the body is subsequently found.

  • Intermediate Scene: Where the body was temporarily stored.

Equipment for Scene Investigation

• Essential tools include:

  • Waterproof aprons and rubber gloves

  • Thermometer

  • Syringe and sterile swabs

  • Hand lens

  • Camera for documentation

  • Trace evidence collection kit (rubber-tipped forceps)

  • Flashlight for visibility.

Sketches and photographs

• Scene of crime should be photographed and video graphed if possible.

• Sketches made.

• Displaced objects, distribution of blood stains, foreign objects to be noted

Collection and Preservation of Evidence

• The items which are most frequently served as evidence:

  • Knives

  • Blunt objects and other instruments

  • Hair and Fibers

  • Firearms and ammunitions like cartridges, wads, sleeves, bullets etc.

  • Broken glass, paper, paint etc.

  • Cigars and cigarette stumps

  • Half eaten fruits or other food stuffs

  • Clothes

  • Chemical substances and poisons

  • Fingerprints and foot prints

  • Blood, semen, saliva, urine, feces and other stains

  • Condoms and condom wrappers

• Blood Stains: Not directly collected as liquids; instead, use gauze soaked in blood and dried.

  • Dried stains scraped for analysis.

  • Invisible blood stains may be detected using luminol.

• Seminal Stains: Collect stains in situ; similar UV light detection for invisibility.

• Other Stains (Urine, Saliva, Feces, Vaginal Fluid): Handled without contamination, following similar protocols.

• Firearms: covered with cotton, packed separately, put in separate containers.

• Fibers: by gloved hands or vacuum suction.

• Material Objects:

  • Collect various evidence types carefully, preventing contamination by using sterile gloves and separate packaging for each item.

Role of Forensic Pathologist

• Actions depend on the availability of forensic support (e.g., photographers, fingerprint experts).

• Rectal temperature measurement is sometimes done in the mortuary due to the nature of violent crimes.

• Careful handling of bodies, especially in conditions like burns or decomposition.

• Transfer of bodies should be done with minimal disturbance, ensuring fragile evidence remains intact.

Crime reconstruction

• Logical analysis of physical evidence and facts to formulate theory regarding actions took place during crime.