9. Bloodstain Pattern Analysis

9. Bloodstain Pattern Analysis Bloodstain Pattern Analysis Is It Blood? • Not always an easy determination. • Stains on clothing: Presumptive & confirmatory testing • Stains not visible: Luminol & blue star • Is it human blood? Drop Shape & Target Surface Blood Spatter May Reveal… • Origin • Distance of bloodstain from target • Direction from which blood impacted • Velocity • Position of victim vs suspect Smooth Surface: Spreads out smoothly. Irregular Surface: Surface tension of spreading edge is broken. • Number of blows/shots Dripping Blood Liquid Blood • Physical Properties • Viscosity • Surface Tension • About the same as water • Behaves as a Projectile in Motion • Gravity as only force: Falls vertically • Gravity and another force: Falls vertically and horizontally General Features • Direction, Angle, Surface Tension, Origin, Movement, Number of Strikes Gravity is the only force acting. Blood drop grows until it can’t anymore Single drop breaks free (tear drop shape) Surface tension pulls in vertically & horizontally Shape settles into sphere (.05 mL) not of break until impact TracingDoes Origin Bloodspots Point of Convergence: 2D, Shows Direction Point of Origin: 3D, Includes Height Tools: Protractor, String, Computer Dripping Pattern Free-falling drops dripping into wet blood Falling from a stationary object Large irregular central stain Small round & oval satellite stains Splash Pattern • Volume > 1 mL • Subjected to LV impact • Thrown Splash Pattern • Tipped • Large central irregular area surrounded by elongated peripheral spatter pattern. Arterial Spurt Pattern • Blood exiting the body under arterial pressure (120 mm Hg); corresponds to heart beating. • Large stains with downward flow on vertical surfaces; air bubbles present if the lung was punctured. • Creates a wave-like appearance. Arterial Spurt Patter Low Velocity Blood Spatter • < 5 ft/s, 1.5 m/s, 3.5 mph • Spot diameter: Mostly 4-8 mm • Free falling drops • Cast off from fist, weapon, etc. • Dripping (blood droplets into themselves) • Splashing (stepping, throwing) • Arterial spurting Medium Velocity Blood Spatter • 25-100 ft/s, 7.5-30 m/s, 17-68 mph • Spot diameter: Mostly 1-4 mm • Blows with weapon (e.g. baseball bat) High Velocity Blood Spatter • > 100 ft/s, 30 m/s, 68 mph • Fine mist: Spot size < .1 mm • Small mass limits spread to 1 m • Some larger droplets reach further • Gunshot: Both back & forward spatter • High speed machinery Other Patterns • Bloodstain patterns that have been altered (objects, gravity, etc.) • Includes wipe, swipe, transfer, and flow patterns Transfer Patterns • Wet, bloodied object contacts a secondary surface • Transfer from: Hand, fingers, shoes, weapons, hair • Transfer to: Walls, ceilings, clothing, bedding • Produces mirror-image of bloodied object Flow Patterns • Blood flows horizontally & vertically • Altered by contours, obstacles • Often ends in pool Transfer Pattern Flow Pattern really