Trauma (Lesson 2.12)

Overview of Trauma in Criminal Investigation

  • Definition of Trauma:

    • Trauma refers to physical injuries inflicted upon individuals during a crime, specifically injuries that involve bodily harm.

    • Emotional trauma, although relevant, is typically excluded from this discussion.

  • Crimes Associated with Physical Trauma:

    • Common crimes resulting in physical trauma include:

    • Assault

    • Rape

    • Battery

    • Murder

  • Types of Physical Trauma:

    • Closed Injury:

    • The skin remains intact.

    • Blood is not visible externally; it is internal.

    • Examples: fractures and bruises caused by blunt force (e.g., punches, kicks).

    • Open Injury:

    • The skin is broken, resulting in visible bleeding.

    • Examples: cuts and wounds from weapons (knives, guns) or impacts (vehicles).

Blood Evidence and Its Significance

  • Blood Evidence:

    • Open injuries lead to blood evidence, essential for crime scene analysis.

    • Blood evidence involves:

    • Composition:

      • Blood type

      • DNA

    • Distribution Pattern:

      • Known as blood spatter, which provides insights into the crime.

  • Information Derived from Blood Evidence:

    • Identification of the type of weapon used (knife, gun, club).

    • Determination of the positions of the attacker and victim during and after the attack.

    • Counting and sequencing of blows delivered to the victim.

    • Insight into the attacker's characteristics (e.g., handedness, blood type, and possible identification via DNA).

Blood Spatter Analysis

  • Production of Blood Spatter:

    • Blood spatter occurs when a force, such as a weapon impact, acts upon a blood source.

    • Types of blood spatter include:

    • Passive Blood:

      • Blood falling solely due to gravity.

    • Projected Blood:

      • Blood forcibly expelled from a wound by impact or internal pressure.

    • Transfer/Contact Blood:

      • Blood transferred to surfaces through wet, bloody objects.

Collection and Documentation of Blood Spatter Evidence

  • Methods of Collection:

    • Photography:

    • Evidence must be photographed from varying distances (long, middle, short).

    • Each image must include a measurement scale.

    • Measurements and Notes:

    • Measure the bloodstain sizes and document their characteristics.

    • Point of Origin:

    • Strings may be placed along some stains to determine where blood originated.

    • Samples:

    • Collect wet or dried blood for typing and DNA analysis.

Physics of Blood Drop Analysis

  • Analyzing Vertical Drops:

    • Blood drops elongate under gravity and resemble a sphere due to cohesive forces.

    • Upon hitting a surface, the drops flatten out and may produce satellite drops (smaller pieces).

    • The diameter of blood spatter increases with height due to increased drop velocity.

    • At approximately 7 ft (2.13 m), blood reaches terminal velocity, causing the diameter to stabilize.

  • Analyzing Angled Drops:

    • Blood striking a surface at an angle results in elongated, elliptical stains.

    • The tail of the droplet indicates the direction of travel.

Calculating the Angle of Impact

  • Methodology:

    • Measure the width (w) and length (l) of a blood spatter.

    • The sine of the angle ($ heta$) is determined by the formula:
      extsine(heta)=racextwidthextlengthext{sine}( heta) = rac{ ext{width}}{ ext{length}}

    • Example Calculation:

    • If width = 5 mm, length = 10 mm, then:
      extsine(heta)=rac510=0.5ext{sine}( heta) = rac{5}{10} = 0.5

    • This corresponds to an angle of $ heta = 30^ ext{degrees}$.

  • Relationship Between Angle of Impact and Point of Origin:

    • Use measured distance (d) and angle ($ heta$) to determine height (h) of blood origin:
      h=dan(heta)h = d an( heta)

    • Example:

    • For $d = 2 ext{ m}$ and $ heta = 45^ ext{degrees}$:
      h=2an(45extdegrees)=2extmh = 2 an(45^ ext{degrees}) = 2 ext{ m}

Analyzing Impact Velocities of Blood

  • Impact Velocity Categories and Associated Drop Sizes:

    • Low Velocities (< 5 ft/s or 1.5 m/s):

    • Produce large drops (4–6 mm in diameter), typical from blunt force impacts.

    • Medium Velocities (5–25 ft/s or 1.5–7.6 m/s):

    • Produce medium-sized drops (1–4 mm), often from stabbings or beatings.

    • High Velocities (> 100 ft/s or 31 m/s):

    • Produce small drops (< 1 mm), characteristic of gunshots.

Specific Blood Patterns

  • Blood Under Pressure:

    • High pressure in arteries causes blood to spurt when a major vessel is cut (e.g., neck).

    • This results in an arc-like pattern on surfaces.

  • Coughing Blood:

    • If blood enters the lungs, the victim may cough and force blood out under pressure—this pattern resembles low- to medium-velocity spatter but may include air bubbles.

  • Cast-off Blood Patterns:

    • In the case of multiple cuts or strikes, blood may be cast off from a weapon as the attacker swings.

    • Backspatter (or blowback) occurs when blood is forced backward upon the impact of a bullet entering a body.

    • Voids: Areas devoid of blood due to obstructions during spatter.

  • Transfer Patterns:

    • Occur when bloody objects contact surfaces, leaving imprints, streaks, or traces.

Conclusion on Bloodstain Analysis

  • Overall Importance:

    • Analysis of bloodstains enables investigators to reconstruct the events of a crime scene, identifying weapons, positions, sequences, and movements involved in the crime.

    • Insight into the type of trauma inflicted correlates directly to crime resolution and prevalence of bodily injury.