How is it a source of forensic evidence?

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Presentation transcript:

How is it a source of forensic evidence? Origin(s) of bloodstain Distance of bloodstain from target Direction from which blood impacted Speed with which blood left its source Position of victim & assailant Movement of victim & assailant Number of blows/shots

Blood Spatter Determining Distance Blood Falls Blood drops fall as small spheres

Blood Spatter Blood drops form different shapes and sizes Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

Blood Spatter Determining Distance Blood Falls Drops form circle when hitting surface Size depends on speed of blood drop

Blood Spatter Determining Distance Blood Falls Faster drop = larger diameter (size) Higher distance = larger diameter Due to air resistance, speed maxes out at distances above about 7 feet

Blood Spatter Determining Distance Blood Falls However, size of drop also depends on the volume of the drop. Volume depends on object blood originated from (needle = small; bat = large)

Blood Spatter Effect of Surface Smooth surface = smooth sphere Rough/porous surface may cause some splatter

Six Patterns Blood can be classified: Passive Fall - Blood falling directly to floor at 90-degree angle will produce circular drops, with secondary satellites being more produced if surface hits is textured

Six Patterns Blood can be classified: Arterial spurts or gushes – typically found on walls or ceilings caused by pumping action of the heart

Six Patterns Blood can be classified: Splashes – shaped like exclamation points. Shape and position of spatter pattern can help locate the position of the victim at the time of the attack

Six Patterns Blood can be classified: Smears – left by bleeding victim depositing blood as he or she touches or brushes against a wall or furniture transfers

Six Patterns Blood can be classified: Trails – can be left by bleeding victim depositing blood as he or she moves from one location to another. Can be round, smeared, appear as spurts

Six Patterns Blood can be classified: Pools – form around victim who is bleeding heavily and remains in one place. If victim is moved to another location, there may be droplets or smearing connecting the first location with a second

Blood Spatter Determining Direction of Blood Narrow end of a blood drop will point in the direction of travel.

Examination of Directionality of Blood Momentum – keeps blood moving in direction it was traveling As droplet moves away from source, it elongates and may produce a thinner, tail-like appearance Tail points in direction of blood’s movement Satellites or secondary drops may appear in front of moving droplet of blood

Blood Spatter and Angle of Impact ANGLE of IMPACT - the acute angle formed between the direction of the blood drop and the plane of the surface it strikes.

Angle of Impact Calculations accurately measuring the length and width of a bloodstain, the impact angle can be calculated using the formula below: sin A = W / L W – Width of blood drop L – Length of blood drop

Blood Spatter Determining Direction of Blood The angle can be determined mathematically. Width/Length, then take the inverse sin (sin-1). This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)

EXAMPLE Finding A LENGTH = 5.9cm WIDTH = 2.6cm

SOLUTION: A = SIN-1 W / L A = SIN-1 2.6/5.9 A = SIN-1 (.44) A = 26.2°

Blood Spatter Determining Direction of Blood If more than one drop (from spatter) results, the point of origin can be determined

Blood Spatter Determining Direction of Blood If more than one drop (from spatter) results, the point of origin can be determined

Blood Spatter Determining Direction of Blood This is a 2-dimensional point of origin. It is possible to determine the 3-D point of origin

Blood Spatter For each blood drop, a string can be guided back to the point of origin.

Area of Origin lies at a point in space above the area of convergence. Measurement of the impact angle allows for translation of the 2-D image (convergence) into a 3-D one (origin).

Area of Origin First measure the distance from each blood stain along its central axis to the AOC (distance = y) Then take the TAN of the degrees A. Third, multiply the TAN of the A by the distance. Measure that distance from the floor up the perpendicular axis and you will arrive at the Area of Origin (AO) FORMULA: AO = TAN (A) x y

Finding AO EXAMPLE GIVEN: DISTANCE FROM BLOODSTAIN (to AOC): 90cm A (calculated from A formula): 30° SOLUTION: = TAN (30°) x 90cm AO = .577 x 90cm = 52cm

Computer Programs Used

Blood Spatter Spattered Blood In general, for higher impacts, the pattern is more spread out and the individual stains are smaller. Low impact = beating High impact = gunshot

Blood Splatter Analysis—Six Patterns Describe each of these based on the images above: a. passive drops b. arterial gushes c. splashes d. smears e. trails f. pools Forensic Science: Fundamentals & Investigations, Chapter 8