jimtrue.com : school : CJT1111 : 2003-07-16: Blood Spatter (Cont.)
Posted by Jim True on July 16, 2003 6:08 AM. Last Updated October 22, 2006 9:23 PM
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Mathematical formula: Tangent of the Angle of the droplet multiplied by the length to the area of convergence; this gives the length from the Area of Convergence to the Area of Origin. Imagine a triangle; if the area of origin is in a straight line outward from the area of convergence (where your blood spatter drops coincide), this leg of the triangle will be at a 90 degree angle to the area of convergence. If you know the length of the from your blood drop to the area of convergence and the angle of the triangle (the blood drop), you can easily calculate the length to the area of convergence as the tangent of your blood drop angle multiplied by the length of the leg of the triangle to the area of convergence to solve for the length of the triangle to the area of origin.
Always pull the Strings first, according to Dave; then do the mathematical calculations to check your work. Otherwise, you will 'cheat' on your string pulling to match your mathematical calculations. Another instructor who testifies in court on blood spatter evidence, doesn't pull strings at all; he only does the mathematical calculations.
Another reason to pull strings: If blood spatter is around a corner, you cannot do the mathematical formula to determine area of origin from the area of convergence, because your area of convergence is in 'space' - there is not a flat plane to measure against to get your leg of the triangle and multiply the tangent of the blood drop angle against.
Perhaps the largest reason to pull strings: jurors just don't get mathematical formulas, unless you can 'prove' it to them visually, with the string pulling.
Always label individual impact patterns with 'letters' not numbers; jurors will confuse the number with the order of impact. Number the individual blood droplets within each impact pattern as A1, A2, A3, A4, A5.
Each individual strike will have it's own pattern, and should be strung separately with different colored string. If all blows are in a simultaneous area, the blood will be primarily spattered on top of itself and it will be almost impossible to determine the separate impacts. You would then use the autopsy report to testify on the number of impacts.
There is NO Average size of an blood drop; it will vary based on the surface area where the blood pools and the amount of blood.
Impact spatters: greater the force, the smaller the droplet of blood. Using the terminology of 'force' instead of 'velocity'. 'Low Velocity' is gravity. 'Medium velocity' is a beating, hammer, baseball bat. 'High velocity' is gunshot or explosion. 25.1 ft per second, low velocity. High velocity is greater than 100 ft per sec. Medium velocity is anything between 25.1 ft and 100 ft per second. Current terminology is 'low, medium and high force' as force causes the impact, velocity is the speed the drops fly away from the surface.
10 percent of blood pattern analysis is stringing the blood. Pattern recognition (determining the instrument that created the pattern, or the instrument that left the pattern, or what the blood pattern can tell us happened) is the biggest portion of blood pattern analysis.
Basic Patterns
Projected blood. (This used to be called 'arterial spray or spurt'; as we are not doctors, we would not know and so we call it 'projected blood'). This is blood that is 'projected' out of the wound by the force of the blood moving through the body. Certain wounds will project further than certain other wounds.
Satellite Droplets. Little drops that break off an original droplet, are called 'satellite droplets'.
Expirated Blood. Small droplets, that look like high velocity (a mist of blood; atomizes the blood, through the force of the impact). Expirated blood, blood being blown out of the lungs or the mouth. Blood mixed with air. There will be air bubbles inside 'expirated blood'. There will not be air bubbles in high velocity blood spatter. Expirated blood landing on a human body however, will react differently, due to the surface texture of the body. The tiny hairs on the human body will break these air bubbles on impact.
Cast off. Blood droplets that follow a path or an arc, in order with the curvature of the movement of the weapon, drops at bottom will be going in one angle, some will be at 90 degrees, and those at the other end of the arc will be going in another direction. There will be two kinds of directionality. A two by four would have two lines of cast off. Difficult to read and often will be in crazy places (cast off will be on ceilings and walls). You will have an 'arc' of cast off. Will tell which way the person is beating, or stabbing and which hand the person is using. If someone is laying there dead and there is cast off, the person has been hit two times. The first strike does damage and the blood pools in the wound, the second strike does cast off.
Walking Droplets. 90 degree droplets straight down, following in a path, one after another; the person was walking slowly. Blood droplets falling into another blood droplet will break the original droplet and 'splash'; they will have satellite drops, with spatter in all kinds of directions, showing that the person stopped. If they stop, you stop until you determine WHY they stopped. Gravity droplets.
Burglar cut himself climbing through the window; could see where he stopped at the door and the dresser. In the living room he stops and his blood is falling into the carpet; the only spot in the house where he could watch all four sides of the house and determine where he was going to leave the house.
Swipe. Contact patterns is where something bloody came in contact with something and moved away. "Swipe" is contact pattern with motion.
Smear. Blood already on the surface and something comes into contact with the bloody area with motion. Swipe is a bloody object; smear is a non-bloody object.
Why is all this terminology so important? When you work a blood scene and you write a report; you will send the blood expert the report and the photographs. We must use the same blood terminology, so an expert can work with the same language.
High velocity, gun shot wound. Chunks of blood, but looks 'atomized'; no air bubbles.
Repetitive contact pattern, person who walks in blood and the repetitive pattern that leaves a specific pattern, but less and less blood afterwards. Like someone stepping in blood and getting it on the bottom of their shoe, the area that came in contact with the blood will continue to leave a 'stamp' of blood as the person walks until there is no more blood on the bottom of their shoe. Something rolling would leave almost the same repetitive pattern but with less blood on the contact print.
Forward spatter (when the projectile goes through an object and sprays in the direction the projectile is traveling). Back Spatter is sprayed backward from the projectile path. forward only occurs when the projectile EXITS. Almost always less back spatter than forward spatter. Back spatter will be very microscopic unless the shot is VERY very close. Also look for 'voids' as they would point out that there would be back spatter on the person who made the shot.
Voids are very important because they demonstrate where something or someone was that MIGHT have blood evidence on them and will demonstrate where the person or thing was in relation to the spatter of blood.
Voids in a v-pattern away from the body, blood hits the leg of the killer and will not go beyond the leg; creating a void. Shoeprints will be from the EMT's checking out the body; a square of blood showing up in luminol, is usually the EMT's kit.
Luminol used in a house where someone has paintedover the top of the blood spatter; will show nothing. Painting over the blood has sealed it. Use an ALS instead, the blood will show up as black, as it absorbs all light.
L-shaped ruler, scale. Pictures must be taken PERFECTLY perpendicular; 90 degrees, so you can guarantee that the patterns can be accurately reproduced in photographs.
Sometimes need to be able to focus your camera without laying down on the floor in a pool of blood to take the picture and focus through the eyepiece. Reverse focusing through a camera; using a flashlight through a camera's viewport.
DRT shot through the heart. Old man is crippled, legs curled up beneath him, on a hospital bed in the living room. Alledgedly asked his wife to go to Wendy's; she came home and found him dead, suspected suicide.
Two blood droplets by his left hand; swipe on his stomach. Closeup shot, burn on his chest. Blood is coming straight down and dripped; he did not move after being shot. One hand above the gun when he shot himself; back spatter on the inside of his hand; contact swipe on his stomach as his hand fell.
Longer the droplet, shorter the angle. Droplets on his lower leg, proved he was standing up.
Wife takes a picture off the wall and throws it at the husband; he's holding the child, he swings the child out of the way. The picture shatters; he goes to put the child on the changer, saw blood on the child, went to lay him on the bed, went to the bathroom instead to wash the blood out of his eyes. Wife tells a different story but her path goes in different direction. Blood droplets were going from left to right which matched the father's story.
Test next week on Blood Spatter.
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