Bloodstain Pattern Analysis Crime Scene Reconstruction

And you think your job is bad

Can be done by: Direct scene evaluation Best done before scene is disturbed Careful study of scene photos The photos MUST be properly done

Information possible Origin of the stain pattern Distances between impact & area of origin Type & direction of impact Object(s) that produced stain(s) # of shots or blows Position of victim, suspect & objects

Position of victim

Object that produced stain

Object that produced stain

Position of object

Movement & direction of victim, suspect & object after bloodshed Support or contradict statements More info for post mortem interval Correlate with pathology findings (arterial spurt)

Movement after bloodshed

Characteristics used Number of spots Their location, size and shape Surface characteristics where stain is deposited

Stain size and shape The tapered end of the drop will point in the direction of travel

Surface Tension A “skin” is formed around the blood drop This causes the surface area of the drop to minimize The drop is spherical – NOT tear drop shaped as they are often shown

Surface tension The drop will oscillate early during the flight but that is quickly damped because of the drop’s viscosity

Average volume of a blood drop There is no average volume of a blood drop Some literature will suggest a volume of .05 ml. The drop volume is directly related to the surface texture from where the blood drops

A different sized drop will form from a machete than will form on the end of a screwdriver

Terminal velocity The maximum speed the blood drop can reach The acceleration rate is offset by air resistance

The larger the droplet the less the effect and the smaller the droplet the greater the effect There will be more smaller drops but they will not travel as much distance

Shape of spot Surface texture is CRITICAL when evaluating the shape of the spot A smooth, hard, non-porous surface will result in less spatter – generally A porous or irregular surface usually results in more spatter

Surface texture The surface texture may vary considerably even if the material is the same

Horizontal motion Directionality can be determined from the stain shape & edge characteristics A tapered or scalloped edge indicates the direction of travel

Horizontal motion & impact angle The greater the horizontal motion (faster) or the lower the impact angle – the more elongated the stain will appear

Horizontal motion & impact angle As the impact angle gets closer to 90° - the “teardrop” pattern is less obvious and the leading edge is determined by small edge scallops

Impact angle & origin Origin can be determined in two dimensions by drawing lines through the individual blood drops along their direction of travel The actual spatter occurred at some point above this 2-D convergence

Impact angle By calculating the impact angle of drops within the stain we can add the third dimension of height This is extremely useful for repositioning a victim- prone, kneeling, standing

Impact angle We are determining the internal angle – the bloodshed occurred within that angle It is impossible for the bloodshed to have occurred outside of that angle

Impact angle By measuring the width and the length of the stain in millimeters – we can calculate the impact angle

Measurement of the stain The stain is measured as an ellipse – a closed curve in the form of a symmetrical oval Be careful measuring the stain Especially as the stains get closer to 90°

To measure a stain Find the widest point of the stain Measure across at that point (mm) From that point measure to the top of the stain (mm) Double the measurement you’ve made to the top

To calculate impact angle Width in millimeters Length in millimeters Width ÷ Length = .something Find the closest # to .something on the sine table

Impact angle & sine table Example Width = 15 mm Length = 30 mm 15÷30 = .50 .50 = 30 degrees on the sine table The stain has an impact angle of 30°

Dripped blood A primary pattern area and small droplets around that area The droplets will not “rebound” high off the impact surface

Dripped blood

Dripped blood – victim standing still

Arterial Spurt

Dripped blood

Cast off blood Smaller droplets Spot size is nearly uniform More of a linear pattern – but not always a straight line Can calculate impact angle to reposition attacker

Spatter evidence - generally Most of the blood will go in the direction of force A lesser amount will come back toward the force Always check those involved for back spatter

Spatter evidence - generally Look for where the blood is…and where the blood isn’t Do you find blood where you would expect to find it? Back spatter will be limited to about 3 feet Spatter found on a suspect puts them in proximity when the blood was shed

Medium force spatter Small droplets – about 1/8th inch or smaller Impact speed of about 5-25 feet per second Consistent with an attack involving a fist, axe, knife, club etc. Consider surface texture

High force spatter Mist-like pattern Like an aerosol spray Do not travel more then 3-4 feet All gunshots, machinery accidents

High force spatter Back spatter – will depend upon: Weapon Ammo Target distance Clothing Location of wound

High force spatter Always check the cuff, sleeve, watch, ring etc. Check the inside of the pants pocket

High force back spatter Will only travel about 3 feet – at best A second shot (into a bloodied area) will increase back spatter

High force – 6 inches in front

High force – 6 inches in back

High force – 12 inches in front

High force – 12 inches behind

A day many waited for