Blood Pattern Analysis Notes

BLOOD PATTERN 101

WHAT IS BLOOD?

  • Blood is a liquid connective tissue.
  • It carries oxygen and removes carbon dioxide (CO2CO_2).
  • It removes waste products from the body.
  • It acts as a defense mechanism.
  • Clotting prevents excessive bleeding.
  • It regulates body temperature.
  • It provides nourishment to the body.

PROPERTIES OF BLOOD

  • COHESION: The mutual attraction between like molecules that causes them to stick together.
  • ADHESION: The mutual attraction between unlike molecules that causes them to cling together.

BLOOD AT A CRIME SCENE

  • Analysis can determine the type of assault.
  • It can help determine the sequence of events.
  • It can allow for convergence and origins of bloodstains to be determined.
  • Analysis helps understand how patterns were produced.
  • It can indicate the position of the victim, assailant, or weapon.

BLOOD IN FLIGHT

  • Blood demonstrates resistance to penetration and separation.
  • A blood droplet is spherical, not teardrop-shaped.
  • A droplet does not break until impact.
  • Larger volume drops travel farther than smaller ones.
  • Drops travel in parabolic paths.

SATELLITE SPATTER

  • Occurs on rough surfaces such as carpet, concrete, or paper.
  • Can happen when blood drips into blood.

ANGLE OF IMPACT

  • The internal angle at which blood strikes a target, relative to the horizontal plane of that target.

CALCULATING ANGLE OF IMPACT

  • You can calculate the approximate angle that the blood came from.
  • Formula: WL=sin⁡A\frac{W}{L} = \sin A, where W = Width, L = Length, and A = Angle.
  • Width/length = sine function of the angle.
  • Measurements should be taken from the center of the blood drop.

ATOMIZED / MISTING

  • A bloodstain pattern resulting from blood reduced to a spray of micro-drops due to applied force.

BLOOD CLOT

  • Fibrinous material resulting from plasma separation as red cells retract from serum.

BLOOD DRIP (AKA DROP)

BLOOD DRIPS

  • DRIP PATTERN: A bloodstain pattern resulting from a liquid that dripped into another liquid, at least one of which was blood.
  • DRIP STAIN: A bloodstain resulting from a falling drop that formed due to gravity.
  • DRIP TRAIL: A bloodstain pattern resulting from the movement of a source of drip stains between two points.

FORWARD SPATTER

  • Blood particles that travel in the same direction as the source of energy or force that caused the spatter.

FORWARD VS. BACK SPATTER

  • Forward spatter travels in the same direction as the force, while back spatter travels in the opposite direction.

CAST-OFF PATTERN

  • A bloodstain pattern resulting from blood drops released from an object due to its motion.

IMPACT SPATTER PATTERN

  • A distribution of blood particles resulting from a single action, traveling in a conical mass prior to landing.
  • The extent or degree of force associated with a pattern may be interpreted by the predominant stain diameters found within the pattern.

BLOOD PATTERNS

  • Projected
  • Flow
  • Expiration
  • Impact
  • Swipe
  • Transfer
  • Void
  • Wipe

PROJECTED

  • A bloodstain pattern resulting from the ejection of blood under hydraulic pressure, typically from a breach in the circulatory system.

SMUDGE

  • A stain that has been distorted to a degree that its history cannot be identified.
  • Chemical enhancement of these stains may yield identifiable patterns.

SWIPE

  • Transference of blood from a moving source onto a previously unstained surface.
  • Direction of motion is usually determined by the feathered edge or accumulation of blood at one end of the pattern.

TRANSFER

  • A pattern created when blood is transferred from one object or surface to another.

VOID

  • An absence of blood in an otherwise continuous bloodstain or bloodstain pattern.

WIPE

  • A pattern created when an object moves through an existing stain, removing and/or altering its appearance.
  • This can also show skeletonization.

DIRECTION OF BLOODSTAIN

  • The direction can be determined from the shape that blood forms when it hits a flat surface.
  • The tail of the elongated drop points to the travel direction.

DIRECTIONALITY OF BLOODSTAINS

  • Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
  • Directionality is usually obvious as the pointed end of the bloodstain (tail) will always point in the direction of travel.

ANGLE OF IMPACT

  • Can be calculated using formula: Angle = inverse of Sin (stain width/length)
  • WL\frac{W}{L} (Inverse of Sin) = angle

TYPES OF STAINS

  • ALTERED
  • INSECT
  • DRIP
  • PARENT
  • PERIMETER
  • SATELLITE
  • SATURATION
  • SERUM
  • SPATTER