Crime Scene Investigation of Blood

Crime Scene Investigation of Blood

Step 1: Looking for Blood

• Luminol

  • Detects traces of blood, even if cleaned.
  • Sprayed on the area to react with iron in blood, producing blue luminescence.
  • Reaction persists for 30 seconds in dark areas.
  • Issues: Other substances can give false positives; the reaction may destroy additional evidence.

• Fluorescein

  • Similar to luminol; ideal for fine stains.
  • Illuminated with UV light, appears greenish-white if blood is present.
  • Can react with copper, bleach, and other substances.

• Light Source

  • High-intensity or UV light is used to find invisible traces of blood and bodily fluids.

Step 2: Confirming it is Blood

• Phenolphthalein
  • Kastle-Meyer test, turns pink when reacting with hemoglobin.
• Leukomalachite (McPail’s reagent)
  • Produces a green/blue color in the presence of blood.
• HemaStix
  • Coated with tetramethylbenzidine (TMB); shows green or blue-green with hemoglobin.

Step 3: Confirm it is Human

• OBTI - Hexagon or ELISA
  • Tests for human blood through antibody-protein reaction.
  • Involves injecting human blood into an animal to produce specific antibodies.

Step 4: Determine Blood Type or Analyze DNA

• Knowledge of blood types (A, B, AB, O) is important.
• Gel Electrophoresis/DNA Fingerprinting
  • Used for detailed DNA analysis.
  • Note: Red Blood Cells lack DNA and nucleus.