jimtrue.com : school : CJT1111 : 2003-07-09: Biological Evidence & Blood Spatter
Posted by Jim True on July 9, 2003 7:29 AM. Last Updated October 22, 2006 9:23 PM
Disclaimer for all material noted here is at the bottom of this web page.
Dave likes blood; considered by some to be an expert in blood spatter interpretation.
Safety - [In biological evidence and crime scene safety]. AIDS, you will not get it working in this stuff. 30 times more likely to get hepatitis; you will get immunizations for hepatitis. 3 sets of shots; only 77% of the shots take. Make sure you go to the doctor and verify that the immunization took.
Study in 1986 done by Rosnick, studying the predecessors to AIDS at that time within blood. HTLV-3, predecessor to AIDS; testing in dried blood to see how long it would be before it would die. 10-15 minutes outside the human body would kill the AIDS virus (at that time). No one knows for sure; the versions are widely variated. Resnick found it still alive 15 days in blood that was dried and exposed to the air.
Any blood you work with, just assume that it carries every damned disease you can think of and be careful. Universal precautions, will be blasted across your call when you go to work a scene where there is danger of infection.
Double-glove; when you walk out of the scene you take your gloves off, but often you leave your gloves on when you open the door, take your gloves off and throw it away and then touch the door unprotected. If you're double-gloved, you will have one pair of gloves on.
Contaminating ourselves: how do you avoid it? Don't mess with the blood. Booties over the shoes or boots. Blood will soak through the booties; everywhere you walk, your car, floor mats of your car. If you take your boots home, don't ever let them inside your house. Plastic tray with water and 10% bleach, set the boots in the tray.
Rubber mats in the car; also cleaned with bleach water.
Extremely careful of big rings; rings will pop through the rubber gloves and expose you to contamination. Diamond rings and engagement rings. Glasses scooting down the nose in the sweat and you push your glasses back up on your face and suddenly you realize you have blood on your nose from the crime scene. Metal watch bands; blood will get stuck inside the band. Get a cheap velcro watch or rubber.
You have to label your evidence; take out your pen, put blood all over your inkpen. Throw your inkpen away.
Equipment used at a blood scene: clean with water and 10% bleach solution. Amway used to have a really good spray that would kill AIDS viruses, germs, etc. Always clean the equipment at the crime scene.
Luminol will react with 1 in a million to 1 in a billion particles of blood.
Keep the booties and place in a separate bag, let airdry and send to the lab.
Packaging: if you have a blood shirt; don't roll that puppy up and put it in a bag. The shirt must dry first. If it's totally sopping wet, will have to put in plastic and take it to work and put it in the drying shed before the putrefaction occurs. When you're packaging, never use staples. Staples will scratch the lab person's arm and he'll get contaminated. Always USE BIOHAZARD sticker. Always airdry and refrigerate. Put paper inbetween every fold of a blood shirt, but never use newspapers.
One word of warning on wearing gloves; when you take the gloves off you will have white powder residue on your hands. Be very careful about where you put your hands after taking the gloves off or you will have residue all over your clothes. Baby wipes are good for cleaning glove residue and fingerprint powder residue.
Blood
Objectives of Blood Stain interpretation; why are we going to study this stuff?
Historical background of blood stain pattern analysis. 1st written documentation; Cain and Abel in the bible, Genesis 4,10.
What's the next big case we know about?
1888, Jack the Ripper. Actually recorded the blood stains in the cases and were actually able to determine the position of the victims when their throats were severed.
1892, Hans Gross wrote a book about Criminal Investigation. Discusses blood stain patterns and is able to determine the directionality of a blood stain by it's shape.
1929, Frenchman, V. Balthazard presented a paper to the 22nd congress of Forensic medicine. Was able to determine the angle of impact of a blood stain by using the width to length ratio.
1955, Dr Paul Kirk. The Fugitive, Samuel Sheppard case. Able to determine relative positions of both the attacker and the victim, and was able to state that the attacker used his left hand to deliver the blows.
1969, Herbert MacDonell. Began an extensive study in blood stain pattern interpretation under the LEAA grant (Law Enforcement Agency Assistance). First person to teach Law Enforcement personnel the techniques of blood stain pattern analysis. Almost all the terminology is accredited to him. His work is also what gave Blood Stain Pattern Analysis the scientific basis for acceptance in court.
You're going to run into an awful lot of violent crime in this line of business; if you can find a sufficient quantity of blood and patterns, there's a lot of specific things about the crime scene you can determine:
Physics
Blood gets thrown up in the air; it will have to come back down based on gravity. Surface tension: liquid will actually be above the rim and not fall off. It has surface tension; any liquid or any fluid mixture has a surface tension to it, all have a different viscosity (thickness); molecules that are the same have a tendency to stick together, this is the surface tension at work. If you touch the surface tension, this will break on the edge.
Rain droplets fall as droplets. Gravity will break surface tension; natural law of science, liquid that has viscosity will stick to itself and hold itself together with surface tension.
Cut on the arm will run down due to gravity, when it gets to the lowest point it will pile up with surface tension until enough collects until gravity will create a drop of surface tension. The drop will fall in a perfect sphere; surface tension forces the molecules back together into a perfect sphere. Balls as it falls. Physical law of nature.
It will stay in that perfect spherical shape until it strikes something that causes it to break.
0.05 ml of blood dropped from different heights. Farther they fall, the bigger they get. Flight Characteristics and Stain Patterns of Human Blood. Published in November of 1971.
About 8 feet and above, they tend to be the same. Terminal velocity, at a certain point it can't go any faster, 25.1 feet per second for 0.05 ml of blood's terminal velocity). Strictly gravity's terminal velocity is 25.1 feet per second. Considered low velocity.
According to the study, the average drop of blood was 0.05 ml of blood, originally. You cannot tell the distance a droplet of blood has fallen from gravity, because you can't tell the actual size of the blood droplet to begin with. Droplet of blood can be any size, depending on the size of the cut.
Surface Texture is probably the greatest influence on blood spatter interpretation. Is the area that the blood droplet hits (the target). Smooth glass, blood leaves a perfect round stain. Carpet, blood goes everywhere. Smoother the surface the easier it is to read this stuff; dictates your pattern.
You can tell by the blood which way the assailant left the crime scene.
You can actually tell by looking at blood on a well and tell where it came from in space (area of origin).
Baseball bat to the person who broke into his house and killed him. Blood spatter analysis voided the suspect's testimony.
Four factors we need to locate the area of origin
Anytime you measure a blood stain pattern, you want to measure scales of feet running across, horizontally, (from a corner or designatable landmark), height is by inches, vertically. A lot easier to determine distance with feet, height with inches. Also helps when doing courtroom testimony, to make sure you always have your photographs oriented correctly.
3 photographs minimum: orientation, no scales; always include your measurement start point. Medium shot, covers most of this. Closeup with just the pattern. Another set with the scales.
Always work with a minimum of 5 droplets.
Information on Blood Stain Pattern Analysis. Lots of articles out there.
Tail always points to the direction the droplet is going.
Toby Wilson (out of Miami-Dade). The 90 degrees is 90 degrees from the surface, whether that be a wall or a floor or ceiling.
Determine Angle of Impact (A) - ARC SIN: Droplet Width (W) / Droplet Length (L). Everyone measures the droplets a little bit differently. Average curve from beginning of drop and create an average curve at the other side for the length. NEVER EVER MEASURE THE TAIL. Can be off to about 30 degrees total. Length is always larger than the width, so the number will always be less than 1 (if 1, it is 90 degrees). Ratio less than one.
Table of Trigonometric Functions - Width / Length and the Arc Sin.
Always say AREA of Convergence. Point of Origin and Point of Convergence is not accurate. Always be going for the size of a soccer ball, or an Area.
Pulling strings allows you to photograph the Area of Origin.
Tools needed for Blood Pattern Analysis:
String in various colors
Pushpins in same colors as strings.
Numbers and/or letters to stick next to blood drops.
Gluesticks
hammers, Nails
rulers - Metric on Blood Spatter
Yarn
Protractor
String Level
Magnifying Loupe with Measuring scale
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