Bloodstains A field of forensic investigation that deals with: – physical properties of blood –patterns produced by forces being applied to blood Blood, as a fluid, follows the laws of physics. A blood droplet will remain spherical until it collides with a surface

The distance between the target surface and the origin of blood. The point of origin of the blood. Movement of a person or an object. The number of blows, etc. causing the bloodshed and/or the dispersal of blood. Type and direction of impact that produced the bloodshed. The position of the victim and/or object during bloodshed. Movement of the victim and/or object after bloodshed. What can bloodstains tell us?

Let’s take a closer look……

Size of the droplet Angle of impact Velocity Height Texture of the target surface  On clean glass or plastic—droplet will have smooth outside edges:  On a rough surface—will produce scalloping on the edges: Conditions Affecting Shape of Blood Droplet

Round—if it falls straight down at a 90 degree angle. Elliptical—blood droplets elongate as the angle decreases from 90 to 0 degrees. Shape of a Blood Drop

Exist in 3 forms: Passive; Impact; Transfer 1.Passive: when natural gravitational forces act on blood. – Can be in the form of: flows, pools, or drips. Ex. Nosebleed Bloodstains

2.Impact: when external forces, other than gravity, act on blood. – Can be in the form of: arterial spurts, castoff, and spatter. a)Arterial Spurts Also known as gushing Blood exiting the body under pressure from a breached artery Bloodstains Cont.

Arterial spurt

Impact: Castoff b)Castoff Created when a volume of blood is flung from an object. Ex. A bloody object (like a hammer) being swung or coming to a sudden stop. Stain starts out circular but becomes more elliptical at the end. Bloodstains Cont.

Cast Off

Bloodstains Cont. c)Backspatter Blood is acted upon by an outside force and broken into smaller stains. Low Velocity: Size is 4-6 mm in diameter – Occurs with a blunt object impact Medium Velocity: Size is 1-4 mm in diameter. – Generally seen in a beating or stabbing High Velocity: Size is < 1mm in diameter. Produces atomized mist (like hairspray). – Typical of gunshot wound

Impact: Spatter (med velocity)

Impact: Spatter (high velocity)

3.Transfer: when an object comes into contact with blood and transfers a patterned image in that blood onto another surface. Can be in the form of: a)Contact Bloody object comes in contact with a clean surface. b)Wipes Blood is on a surface (and beginning to dry) and is wiped or smeared. c)Swipes Blood is transferred from a moving source onto an unstained surface Bloodstains Cont.

Transfer: Contact

Transfer: Wipe

Transfer: Swipe

Measuring the Angle of Impact: The more acute the angle of impact, the more elongated the stain and the easier it is to determine the direction of travel. 90 degree angles are perfectly round drops Acute degree angles (Ex. 30 degrees) have an elliptical shape and will begin to produce a tail/spine. Bloodstain Pattern Analysis

90 0 angle 30 0 angle Tail/Spine

Stain tails point in the direction that the blood drop was traveling.

Identify the bloodstains you will use. Measure the width and length of each stain. Apply the following formula: width = sine of angle impact length Determining Angle of Impact W L inverse sine (arcsine) = Angle of Impact (in degrees)

The greater the difference between the width and length, the sharper the angle of impact. Ex. Imagine a bloodstain 2 mm wide and 4 mm long. The width divided by the length is 0.5 The arcsine of 0.5 is 30 So the blood hit the surface at a 30 0 angle. Determining Angle of Impact W L

Based on trig functions of right triangle Angle of Impact will always be 90 o or less. Determining Angle of Impact SIN = Opposite / Hypotenuse COS = Adjacent / Hypotenuse TAN = Opposite / Adjacent

The area of convergence is the point of origin - the spot where the “blow” occurred. The location of the blood source can be determined by drawing lines from the various blood droplets to the area where they intersect. ** Area of Convergence will NEVER come together at a single point. Area of Convergence

Determining Point of Origin Area of ConvergenceImpact Site Point of Origin Tan of Angle of Impact x Distance to Convergence = Distance From Surface Distance

A blood droplet will remain spherical in space until it collides with a surface. Once a blood droplet impacts a surface, a bloodstain is formed. How will the shape change as the height is increased or decreased? Blood Droplet Characteristics