Blood Forensics CHS Forensics Blood Volume n On
Blood Forensics CHS Forensics
Blood Volume n On average, blood accounts for 8% of a persons total body weight n 5 to 6 liters of blood for males n 4 to 5 liters of blood for females
Blood Volume n. A 40 percent blood volume loss, internally or/and externally, will result in irreversible shock (death). n A blood loss of 1. 5 liters, internally or externally, causes incapacitation.
forensic serologist n Determination of the type and characteristics of blood n blood testing n bloodstain examination
forensic serologist n Their main job is preparation of testimony or presentations at trial n Also analyzes n semen, n saliva, n other body fluids and may or may not be involved with DNA typing.
Blood Forensics n Blood is the most common, wellknown, and perhaps most important evidence in the world of criminal justice today. n Its presence always links suspect and victim to one another and the scene of violence.
Stain Patterns of Blood
To Be Considered n Origin(s) of bloodstain n Distance of bloodstain from target n Direction from which blood impacted n Speed with which blood left source n Position of victim and assailant n Movement of victim and assailant n Number of blows/shots
Surface Tension & Blood Drops n Slightly less than that of water n Tends to form into sphere in flight (not the artistic teardrop shape) n Result of surface tension that binds molecules together n Elastic-like property of surface of liquid makes it contract
Surface Tension & Blood Drops More rapid bleeding: may make slightly larger drops n BUT, slower bleeding: not always result in smaller drops § n Cast from a moving source n Consists of smaller droplets n Behaves as projectile in motion n Obeys the laws of physics and mathematics n
Stain Patterns of Blood n Interpretation and reconstruction events that produced the bleeding n Location n Distribution n Appearance of bloodstains and spatters
Stain Patterns of Blood n Determination of direction, dropping distance, and angle of impact n Surface texture n Shape, size n Location
Stain Patterns of Blood n Surface texture n Paramount importance n Harder and less porous the surface the less spatter results vary n Direction of travel of blood striking an object n Pointed end of bloodstain always faces direction of travel
Stain Patterns of Blood n Impact angle of blood on a flat surface n Measure degree of circular distortion n At right angles blood drop is circular n Angle decreases stain becomes elongated
Perpendicular to Surface n Blood strikes perpendicular (90 degrees) n Bloodstain circular n Length and width of stain will be equal 90○ ANGLE
Acute Angle to Surface n Angle less than 90 degrees n Elongated or a tear drop shape 70○ ANGLE
More Examples n 45○ ANGLE n 30○ ANGLE n 10○ ANGLE n 5○ ANGLE
“Fitting” of a ellipse in blood Tail or spine Parent Drop
Stain Patterns of Blood n Origin of a blood spatter in a twodimensional configuration n Draw straight lines through the long axis of several individual bloodstains n Intersection or point of convergence of the lines origin point
Point of Convergence n Common point n 2 dimensional surface n. Over which the directionality of several bloodstains can be retraced
Point of Convergence n Directionality of a group of stains determined n. Possible to determine a 2 D point (or area) for the group of stains n Point of convergence determined by n. Drawing a line through the long axis of a group of bloodstains
Point of Convergence (2 D)
Blood Spatter Analysis 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
Point of Origin n Lies at a point in space n Above the point of convergence n Measurement of the impact angle allows for translation of the 2 -D image (convergence) into a 3 -D one (origin)
Point of Origin n To determine n n n 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 (3 D --- use Z axis)
Modern Analysis with Computer
Categories of Blood Stains
Passive n Drops created or formed by the force of gravity acting alone n Examples n Passive Drops n Drip Patterns (blood driping into blood) n Pools
Passive Blood Spatter
Transfer n Created when a wet, bloody surface comes in contact with a secondary surface n Examples n Swipe or smear n Wipe n Pattern transfer
Passive Transfer A recognizable image of all or a portion of the original surface may be observed in the pattern.
Projected n Created when an exposed blood source is subjected to an action or force, greater than the force of gravity n Examples n Arterial spurt/gush n Cast-off n Impact spatter
n Void n Skeletonized n Expirated Blood stain
Velocity
Low Velocity (usually >4 mm) n Relatively large stains 4 mm in size and greater n Gravitational pull up to 5 feet/sec
Medium Velocity n Most stains 1 to 4 mm in size n Force of 5 to 25 feet/sec
High Velocity (usually < 1 mm) n Most stains 1 mm or less (much variability) n Force of 100 feet/sec or greater
Cited www. sd 281. k 12. id. us/thornton n Phillips. Chemistry Concepts and Applications Teachers Wraparound Edition (Glencoe Science). New York: Glencoe/Mcgraw-Hill, 2004. Print. n
Pictures n n n n http: //nobelprize. org/nobel_prizes/medicine/laureates/1930/landsteiner. jpg http: //www. ncbi. nlm. nih. gov/projects/genome/guide/img/rhesus. jpg http: //virtualbiologytutor. co. uk/images/erythrocytes. jpg http: //www. scientificpsychic. com/mind/leukocytes 0. jpg http: //student. ccbcmd. edu/~gkaiser/TOC/eukaryotic. html http: //www. coca-cola-2 -liter-botle. hemospat. com
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