In-Depth Notes on Biological Evidence in Forensic Science

Biological Evidence

Overview of Biological Evidence

  • Biological evidence is crucial in forensic science to establish connections to a crime.

  • Common types include:

  • Buccal swab (inside cheek)

  • Blood (includes both liquid and dried stains)

  • Semen

  • Vaginal swabs

  • Hair (must include root sheath)

  • Bone

  • Tissue

  • Urine

Forensic Serology

  • Definition: Forensic serology involves examining and analyzing bodily fluids to identify their presence.

  • Process:

  • Locate the body fluid at a crime scene.

  • Identify it as biological evidence.

  • Distinction: Serology finds evidence of fluid; DNA analysis matches fluids to an individual specific.

Importance of Serology in Forensic Analysis

  • Medical vs. Forensic Analysis:

  • Medically, bodily fluids are analyzed for health assessment.

  • Forensically, the focus is on determining the source of fluids at crime scenes.

  • DNA specifics: Provides detailed information regarding the biological material’s origin, aiding in case reanalysis.

Blood Evidence

  • Types of Testing:

  • Presumptive Testing: Initial tests that provide indicators of blood presence but not definitive proof. These tests involve visible changes (like color or luminescence).

  • Follow up with Confirmatory Tests for definitive identification.

  • Importance of Presumptive Tests:

  • Cost-effective and quick.

  • Allows initial assessment before detailed DNA tests.

  • Blood is characterized as an extracellular fluid comprising organic/inorganic materials. Hemoglobin gives blood its red color.

Common Presumptive Tests for Blood

  • Examples include:

  • Kastle-Meyer test

  • Hemastix®

  • Field Characteristics: Typically exhibits a color change from yellow to green or blue-green.

Chemoluminescence and Fluorescence Testing

  • Processes:

  • Apply chemical mixtures to surfaces being tested and observe in darkness or with an Alternate Light Source (ALS).

  • Determine limitations and details of stains while assessing contamination risks.

  • Types:

  • Chemoluminescence (e.g., Luminol/Blue Star): Light emitted from chemical reactions.

  • Fluorescence: Enhanced visibility when exposed to specific wavelengths of light.

Semen Evidence

  • Composition: Semen primarily consists of spermatozoa, which are characterized by:

  • A flagellated structure composed of the head, midpiece, and tail.

  • Detection Methods: Identification involves noting stains or conducting specific crystal tests.

Saliva Evidence

  • Composition: Saliva is an alkaline secretion that contains water, mucus, proteins, salts, and enzymes.

  • Production: The average individual produces 1 to 1.5 liters of saliva daily.

  • Function: Aids digestion of starches; can be detected by measuring the enzyme alpha-amylase in high concentrations (50 times higher in saliva).

  • Saliva can remain detectable for up to 28 months.

Alternate Light Sources (ALS)

  • Role: Used to locate biological stains like semen, saliva, urine, and vaginal fluids through various wavelengths of light.

  • Limitations: While ALS indicates where critical evidence could be, it does not identify the specific type of stain.

  • Technological Advances: Continuous improvements in ALS technology have enhanced the ability to detect various bodily fluids, but each test comes with limitations. Understanding historical contexts helps shape future advancements in forensic methods.