Module 2: Bloodstain Pattern Analysis - Classifying Patterns

Classification of Bloodstains

Definition and Importance of Bloodstains

  • Spattered Blood

    • Defined as a random distribution of bloodstains that vary in size.

    • Can be produced by a variety of mechanisms.

    • Quantity and size of spatters can vary significantly based on conditions.

    • Amount of available blood affects spatter size range.

    • Force applied to blood must overcome surface tension to create spatter.

  • Importance of Bloodstain Analysis

    • Helps determine the area or location of the blood source.

    • Presence on a suspect's clothing may place the suspect at the scene.

    • Allows determination of the mechanism that created the spatter pattern.

Categories of Bloodstains

  • Bloodstain patterns can be categorized as:

    • Spatter Stains

    • Non-Spatter Stains

Spatter Stains

  • Occur when a blood mass is broken into droplets and put into free flight by some mechanism.

  • Resulting circular or elliptical shaped stains when droplets strike surfaces.

  • Examples of spatter patterns include:

    • Impact Spatter

    • Cast Off Patterns

    • Spurts

    • Drip Trails

Related Spatter

  • Crime scene technicians establish relationships among spatter through three characteristics:

    • Impact Angle

    • Directional Angle

    • Proximity

  • Patterns recognized through training and experience.

Spurts

  • Created when blood is ejected in a stream under pressure.

    • Commonly occurs when arteries or the heart are breached (termed Arterial Spurting).

  • Orientation of stains is typically linear or curvilinear.

  • Large volume characterizes individual stains.

  • Reflects blood volume ejected correlated with heartbeats.

  • Provides insights into victim's movement or orientation post-injury.

Cast Off Patterns

  • Created when blood is flung from a moving or suddenly stopping object.

    • Typically associated with swinging weapons.

  • Series of related spatter stains deposited in linear or curvilinear orientations.

    • Consistent parallel directional angles correlated to motion.

  • Helps determine the orientation and minimum number of swings of the bloodied item.

Drip Trails

  • Patterns demonstrating movement initiated by a dripping item from point A to point B.

  • Linearly distributed spatter stains with consistent size ranges (3 to 25 millimeters).

  • Directionality consistent with gravity, indicating movement paths of individuals or objects.

Impact Patterns

  • Radiating patterns of small circular or elliptical stains due to force breaking blood at the source.

  • Related small spatter stains exhibit radiating distribution without substantial changes in stain shape.

    • Stain sizes range from sub-millimeter to 4-5 millimeters.

    • Can range from few to thousands of stains.

  • Occurs from an impact displacing a blood source (gunshot, blunt trauma).

    • Two subcategories:

    • Mist: Stains < 1 millimeter, typically from high force impacts (explosive, gunshot).

    • Expiratory Spatter: Blood mixed with air bubbles during victim's exhalation may create small droplets.

Drips

  • Result from blood dripping from an individual or bloodied object.

  • May comprise one or more spatter stains with diameter (3-25 millimeters).

  • Random orientation on surfaces, with directional angle aligned to gravity.

  • Less distinct than drip trails but still provide info about the scene.

Non-Spatter Stains

  • Stains with no circular/elliptical shapes, but may contain secondary spatter.

  • Patterns include:

    • Gushes

    • Blood into blood patterns

    • Contact stains (smears, wipes, swipes, pattern transfers)

Gushes

  • Occur when large volumes of blood are ejected, leading to accumulation and satellite spatter presence.

  • Irregular margins and may resemble spurts but are classified as non-spatter.

Blood into Blood Patterns

  • Results from spatter of blood deposited into or onto another liquid, leading to secondary spatter.

  • Occurs typically when a dripping object is stationary for a period.

Contact Stains

  • Transferred from one object to another through contact.

  • Variations include:

    • Smears: Blood transferred due to contact, with irregular margins.

    • Wipes: Smearing through a pre-existing stain (movement over existing blood).

    • Swipes: Smearing deposited onto a surface.

    • Pattern Transfers: Stain created by the transfer of blood from one object exhibiting recognizable characteristics.

    • May include hand/foot prints or patterns from weapons.

Blood Pools and Flows

  • Help establish the position and movement of bleeding individuals.

  • Flows obey gravity and abnormal patterns may indicate movement before death or disturbance.

Saturation Stains

  • Occur when blood is absorbed into a permeable surface.

  • Rarely provide specific information and may destroy patterns of interest.

Additional Patterns

  • Fly Spots: Resulting from flies transferring blood in a scene, can mimic impact spatter.

  • Voids: Areas lacking staining surrounded by blood patterns, indicating the presence of obstruction or secondary objects during blood spatter events.

  • Voids can aid in understanding relative positioning at the time of the event.