Forensic Science Quiz: Blood Identification

History

• Edmond Locard (1877-1966): Proposed the exchange principle, "every contact leaves a trace."
• Karl Landsteiner (1901): Discovered ABO blood groups.
• Ludwig Teichman (1853) Developed the first confirmatory test for hemoglobin.
• Paul Theodor (1901): Published the first method for distinguishing between human and animal protein.
• Leones Lattes (1915): Developed methods for grouping dried blood stains.
• Landsteiner and Weiner (1915): Identified Rhesus blood factors.
• A. Ochterlony (1949): Developed the Ouchterlony species identification test.
• Stuart Kind (1960): Introduced tests for species identification using mixed agglutination techniques.
• Brian Culliford (1964): Identified polymorphic variants of the phosphoglumutase (PGM) enzyme.
• Alex Jefferies (1984): Published seminal work on DNA fingerprinting, developing restriction fragment length polymorphism (RFLP).
• Kary Banks Mullis (1986): Invented the polymerase chain reaction (PCR).
• Herbert Leon MacDonell (1971): Outlined rules of blood spatter evidence, including the terminal velocity of a falling blood drop.
• Eduard Piotrowski (1985): Published the first official studies on blood stain patterns.
• Alexandre Lacassagne: Contributed to the study of gunshot wounds.
• Victor Balthazard (1939): Studied blood spatter patterns.

Important Time Frames

• 1800s: Early attempts to identify blood stains using microscopy and tests for hemoglobin.
• 1923: DC court rejected the scientific validity of the polygraph test.
• 1955: State of Ohio v. Samuel Sheppard case: Blood spatter evidence suggested a third party was present at the crime scene, but Sheppard's DNA was excluded from testing.
• 1963: Brady v. Maryland case: The prosecution's withholding of a co-defendant's confession was ruled suppression of evidence favorable to the defense.
• 1970s: Research identified polymorphic variants for several serum proteins and blood enzymes.
• 1972: Giglio v. US case: Evidence from a co-conspirator was deemed unreliable due to his plea deal.

Presumptive Blood Tests

• Leucomalachite Green:
  • Indicator color: GREEN
  • Low Sensitivity
  • Most common presumptive test
  • Reagent: Sodium perborate, leuco malachite green, glacial acetic acid and water
  • Procedure: Add few drops of reagent to filter paper swipe of stain, then add H2O2. A rapid color change indicates blood.
• Luminol:
  • Indicator: FLUORESCENCE
  • Very high sensitivity
  • Reagent: 5-amino-2,3-dihydro-1,4-phthalazinedione
• Hemastix:
  • Used by responding officers at crime scenes or hospitals.
  • Reagent stick is touched to suspected stain and water is added. A green color indicates blood.
  • Can give false positives for gun powder residues.
  • May be discouraged due to potential for interfering with DNA analysis.

Confirmatory Tests for Blood

• Confirms the presence of blood.
• Microchemical Tests:
  • Confirm the identity of a positive presumptive test for blood.
  • Takayama or Hemochromogen Test: Red feathery crystals of pyridine ferroprotoporphyrin form when ferrous iron from hemoglobin reacts with pyridine and are observed under a microscope.
  • Teichman Reaction: Similar to the Takayama test, but the Takayama test is preferred due to easier crystal formation.
• Microscopy:
  • Used to verify the presence of blood cells in a suspected blood sample.
  • Dried stains require reconstitution, re-drying, fixing, and staining for microscopy.
  • The effectiveness of this method depends on the analyst's expertise and the condition of the stain.
• Spectroscopy:
  • Distinguishes between hemoglobin and hemoglobin derivatives.
  • Reliable for older stains that tested negative with other methods.
  • All hemoglobin derivatives exhibit a strong absorbance at 400-425 nm (Soret band).
• Hematrace ABAcard Tests:
  • Detects the presence of human hemoglobin.
  • Based on antibody-antigen reactions between the sample and antibodies in the test card.
  • Positive results have been reported for ferret blood.

Touch DNA

• Factors impacting probative results from touch DNA:
  • Shedders vs. Non-shedders: Some individuals shed more skin cells than others. Sweating can increase DNA transfer.
  • Surfaces touched: Rough textures increase friction and DNA transfer. Larger surface areas result in more DNA transfer.
  • Length of time touched: Repeated contact increases DNA transfer.
  • Number of people touching the item: Items touched by multiple people may have complex DNA mixtures.
  • Presence of other DNA sources: Items with blood or other body fluids may have overwhelming amounts of DNA.

Factors Affecting Touch DNA Sample Collection

• Surface type: Rough or textured surfaces may require multiple swabs.
• Size of the surface: May require more than one swab.
• Cleanliness of the surface: Wet swab followed by dry swab may be necessary.
• Latent print request: Latent print processing can dilute DNA samples.
• Presence of other DNA: Items with blood or other body fluids should not be tested for touch DNA unless the fluid is swabbed separately.

Laboratory Analysis of Biological Samples

• Electrophoresis:

  • Separates molecules based on electrical charge and size.
  • Positively charged molecules move to the cathode, negatively charged molecules move to the anode.
  • Used in forensic science to identify biological markers for personal identification and in DNA analysis.
  • Can be used to detect variations in protein charge from amino acid substitutions.
  • Visualization:
    • Hemoglobin is naturally colored.
    • Other proteins, antibodies, and enzymes require staining with Ponceau red, Amido black, or Coomassie blue.

• Species Typing:

  • Used to identify blood proteins specific to each animal species.
  • Relies on antibody-antigen interactions.
  • Ouchterlony Double Diffusion:
    • Popular species determination test using immunodiffusion and precipitation.
    • Antigen and antibody are added to separate wells in an agarose gel.
    • Forming precipitin lines where antigen-antibody reactions occur.
  • DNA Testing:
    • Identifies human DNA using oligonucleotide probes that hybridize to human DNA immobilized on a nylon membrane.

Blood Stain Patterns

• Blood motion:

  • Cohesive forces create surface tension in blood drops, resisting penetration.
  • Blood drops in air are spheroidal.

• Directionality:

  • Blood spatter patterns provide information about the sequence of events, droplet directionality, and movement.
  • A blood drop's trajectory is influenced by its contact angle with the surface and the force it hits with.

• Clot formation and bruising:

  • Homeostasis: The body's process of stopping bleeding. Consists of vasoconstriction, platelet activation, and coagulation.
  • Platelets: Irregularly shaped, colorless cells that form clots to stop bleeding. Release fibrinogen which forms a mesh-like web to trap blood cells.
  • Bruising: Caused by bleeding under the skin when superficial blood vessels are damaged. The color changes with age, progressing from black/blue to green/yellow.