Bloodstain Pattern Analysis and Spatter Interpretation

Bloodstain Pattern Analysis Blood Spatter Interpretation ● The significance of the significance of the location, position, and shape of bloodstain patterns Reasons for Interpreting ● Possible moments of people ● Possible positions of people ● Possible reconstruction of events ○ Direction from which originated ○ Minimum number of blows that struck victim Spatter Dynamics ● Result of a force interacting with a pool of blood ● Assumes A Straight-Line Trajectory ● Directionality and angularity can be determined ● The following must be taken into account when performing blood spatter analysis: ○ Surface Texture ■ The harder and less porous the surface, the less spatter will result. ■ Blood on wood might be soaked up a bit more bc of the surface. ○ Direction of travel ○ Impact angle Satellite Spatter ● Produced when blood droplets strike another object or a pool of blood, resulting in a distribution of patterns around the parent stain. Direction of Travel ● The direction of travel of the blood drop can be determined by the stain’s shape. ● The pointed end of a bloodstain always faces in the direction the blood was traveling. Impact Angle ● The angle the blood drop impacts a surface can be determined by measuring the length and width of the stain. ● A circular shaped stain is caused by blood hitting a surface at a right 90 degree angle. ● An elongated shape impacted the surface at an angle that was less than 90 degrees. ● The impact angle is calculated using the following formula: ARC SIN (W/L) ○ W= Width of the stain ○ L= Length of the stain ● The origin of the blood spatter found at a crime scene can be established by examining individual blood drops. ● On a 2D surface, straight lines can be drawn through the long axis of several stains, following the line of their tails. ● The intersection or area of convergence of the lines represents the point from which the blood originated. ● It may also be useful to determine the area of origin of a pattern in a 3D space. ● This can show the approximate position of the victim or suspect when the pattern was created. ● Once the area of convergence is found, the impact angles of the blood drops are determined. ● The String method can then be used to examine the blood drops and determine the area of origin.’ Types of Spatter Patterns Low Velocity Spatter ● Consisting of drops with diameters of 4mm or MORE ● Normally produced by gravity, minimal force, or by an object dropping into a pool of blood and splashing blood Medium Velocity Spatter ● Consisting of small drops with diameters from 1-4 mm ● Normally associated with blunt force trauma High Velocity Spatter ● Consisting of very fine drops with diameters less than 1mm. ● Can be produced by gunshot wounds or explosions. Other Types of Spatter Patterns ● Gunshot: Void pattern Cast off Spatter ● Created when a bloody object flings blood in an arc onto another surface ● Cast off patterns show the minimum number of blows Arterial Spatter ● Projection of blood spurts .. missing Contact/ Transfer Patterns ● This pattern is produced when a bloody object touches an object that does not have blood on it. ● These patterns usually do not involve additional movement. Swipe Pattern ● A Swipe pattern is produced when a bloody object moves across a surface. Flow Pattern ● A pattern made by drops flowing with the pull of gravity. Drip Trail Patterns ● A series of drops that are formed by blood. ● Dripping off an object or blood dripping from a wound. ● The stains form a line or path that can show the movement of the individual or object. Documenting Blood Spatter Evidence ● Blood spatter evidence should be MISSING ● Photographs and sketches of the overall patterns should also be created to show the orientation of the patterns to the scene. ● The Perimeter Ruler Method can be used to document bloodstain patterns. ○ Large rulers are used to show scale in the overall photos. ○ Small Rulers are used to show scale in the close up photos. Experiment #7 DUE APRIL 6 Part A: Impact Angle Determination In this exercise you will calculate the impact angle of several drops left behnd at a crime scene. 1. Measure the length and width of each stain (in cm) Note: For elongated stains, the tail is not included in the measurement of the length. Result should between 1 degree to 90 degree. If answer is .63, Change to degree.