Biological Stain Analysis

Overview

• Key topics related to blood analysis in forensics:
  • Blood characteristics
  • Detecting blood at a crime scene
  • Tests on blood
  • Seminal stains detection and confirmation
  • Evidence related to sex crimes

Nature of Blood

• Blood is a complex mixture of:
  • Cells
  • Enzymes
  • Proteins
  • Inorganic substances
• Plasma:
  • Fluid portion of blood, mainly composed of water.
• Solid components in plasma include:
  • Red blood cells (erythrocytes)
  • White blood cells (leukocytes)
  • Platelets
• Antigens on red blood cells are responsible for blood type characteristics.

Red Blood Cells (Erythrocytes)

• Also known as:
  • Red blood corpuscles
  • Haematids
  • Erythroid cells

Blood Typing

• More than 15 blood antigen systems exist; the most relevant in forensics are:
  • A-B-O System
  • Rh System
• Blood types:
  • Type A: A antigens on red blood cells, Anti-B antibodies
  • Type B: B antigens on red blood cells, Anti-A antibodies
  • Type AB: A and B antigens, no antibodies
  • Type O: No A or B antigens, Anti-A and Anti-B antibodies
• Rh factor:
  • Determined by the presence of the D antigen.
  • Rh positive individuals have the D antigen; Rh negative do not.

Blood Tests

• Kastle-Meyer Color Test:
  • Positive result suggests the presence of blood due to deep pink color from hemoglobin.
• Luminol Test:
  • Detects trace amounts of blood; reacts with heme to produce luminescence.
• BlueStar Test:
  • Similar to Luminol in interaction with heme.
• Microcrystalline Tests (Takayama, Teichmann):
  • Involve specific chemicals that create characteristic crystals from blood.

Blood Origin Testing

• Precipitin Test:
  • Determines if stain is from human or animal origin.
• Gel Diffusion Technique:
  • Antigens and antibodies move towards each other on an agar plate, forming visible precipitation if human blood is present.

Individualizing Bloodstains

• After confirming a stain is human blood, forensic scientists use DNA analysis to link it to a specific individual.

Testing for Seminal Stains

• Important in sexual offenses investigations.
• Acid Phosphatase Test:
  • Detects an enzyme unique to seminal fluid, indicated by a purple coloration.
• Semen can also be identified via:
  • Presence of spermatozoa
  • Presence of protein p30 unique to seminal plasma.

Evidence Collection in Sex Crimes

• Immediate medical examination post-assault is critical.
• Essential evidence includes:
  • Clothing
  • Hairs
  • Vaginal and rectal swabs
• Packaging must be done carefully (e.g., using paper bags).

Evidence Collection Protocols

• Involves collecting:
  • Outer & undergarments
  • Bedding
  • Other physical evidence from the scene
• Suspect items typically collected:
  • All clothing
  • Hair samples
  • Blood or buccal swabs for DNA analysis

Summary

• The ability to detect, analyze, and interpret blood characteristics and seminal stains is fundamental in forensic investigations, particularly in cases involving violent crimes and sexual offenses. Accurate testing and evidence collection are paramount for successful legal outcomes.