Blood Forensics CHS Forensics

Blood Volume On average, blood accounts for 8% of a persons total body weight 5 to 6 liters of blood for males 4 to 5 liters of blood for females

Blood Volume A 40 percent blood volume loss, internally or/and externally, will result in irreversible shock (death). A blood loss of 1.5 liters, internally or externally, causes incapacitation.

forensic serologist Determination of the type and characteristics of blood blood testing bloodstain examination

forensic serologist Their main job is preparation of testimony or presentations at Also analyzes semen, saliva, other body fluids and may or may not be involved with DNA typing. trial

Blood Forensics Blood is the most common, well- known, and perhaps most important evidence in the world of criminal justice today. Its presence always links suspect and victim to one another and the scene of violence.

Stain Patterns of Blood

To Be Considered Origin(s) of bloodstain Distance of bloodstain from target Direction from which blood impacted Speed with which blood left source Position of victim and assailant Movement of victim and assailant Number of blows/shots

Surface Tension & Blood Drops Slightly less than that of water Tends to form into sphere in flight (not the artistic teardrop shape) Result of surface tension that binds molecules together Elastic-like property of surface of liquid makes it contract

 Surface Tension & Blood Drops More rapid bleeding: may make slightly larger drops BUT, slower bleeding: not always result in smaller drops Cast from a moving source Consists of smaller droplets Behaves as projectile in motion Obeys the laws of physics and mathematics

Stain Patterns of Blood Interpretation and reconstruction events that produced the bleeding Location Distribution Appearance of bloodstains and spatters

Stain Patterns of Blood Determination of direction, dropping distance, and angle of impact Surface texture Shape, size Location

Stain Patterns of Blood Surface texture Paramount importance Harder and less porous the surface the less spatter results vary Direction of travel of blood striking an object Pointed end of bloodstain always faces direction of travel

Stain Patterns of Blood Impact angle of blood on a flat surface Measure degree of circular distortion At right angles blood drop is circular Angle decreases stain becomes elongated

Perpendicular to Surface Blood strikes perpendicular (90 degrees) Bloodstain circular Length and width of stain will be equal 90 ○ ANGLE

Acute Angle to Surface Angle less than 90 degrees Elongated or a tear drop shape 70 ○ ANGLE

45 ○ ANGLE 30 ○ ANGLE 10 ○ ANGLE 5 ○ ANGLE More Examples

“Fitting” of an ellipse in blood drop Tail or spine Parent Drop

Stain Patterns of Blood Origin of a blood spatter in a two- dimensional configuration Draw straight lines through the long axis of several individual bloodstains Intersection or point of convergence of the lines origin point

Point of Convergence Common point 2 dimensional surface Over which the directionality of several bloodstains can be retraced

Point of Convergence Directionality of a group of stains determined Possible to determine a 2D point (or area) for the group of stains Point of convergence determined by Drawing a line through the long axis of a group of bloodstains

Point of Convergence (2D)

Figure 12–13 Illustration of stain convergence on a two-dimensional plane. Convergence represents the point from which the stains emanated. Courtesy Judith Bunker, J. L. Bunker & Assoc., Ocoee, FL Blood Spatter Analysis

Point of Origin Lies at a point in space Above the point of convergence Measurement of the impact angle allows for translation of the 2-D image (convergence) into a 3-D one (origin)

Point of Origin To determine Measure distance from each blood stain along its central axis to POC (distance = y) Find tangent of impact angle ( tan θi ) Multiply the TAN of the AOI by the distance Measure that distance from floor up the perpendicular axis and you will arrive at the Point of Origin (PO) FORMULA: PO = y · tan θi

Point of Origin (3D --- use Z axis) Point of Origin

Modern Analysis with Computer

Categories of Blood Stains

Passive Drops created or formed by the force of gravity acting alone Examples Passive Drops Drip Patterns (blood driping into blood) Pools

Passive Blood Spatter

Transfer Created when a wet, bloody surface comes in contact with a secondary surface Examples Swipe or smear Wipe Pattern transfer

A recognizable image of all or a portion of the original surface may be observed in the pattern. Passive Transfer

Projected Created when an exposed blood source is subjected to an action or force, greater than the force of gravity Examples Arterial spurt/gush Cast-off Impact spatter

Void Skeletonized stain Expirated Blood

Velocity

Low Velocity (usually >4 mm) Relatively large stains 4mm in size and greater Gravitational pull up to 5 feet/sec

Medium Velocity Most stains 1 to 4mm in size Force of 5 to 25 feet/sec

High Velocity (usually < 1mm) Most stains 1mm or less (much variability) Force of 100 feet/sec or greater

Cited Phillips. Chemistry Concepts and Applications Teachers Wraparound Edition (Glencoe Science). New York: Glencoe/Mcgraw-Hill, Print.

Pictures hemospat.com