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Blood Evidence
Blood Evidence Review Topics Forensics
| Question | Answer |
|---|---|
| Plasma % | 55% |
| Red Blood cells % | 41% |
| White Blood Cells % | 4% |
| Red Blood cells lose their ___ when they are being produced in the Bone Marrow | nucleus |
| Only _______ contain nuclear DNA | White Blood cells |
| Serology | Term used to describe a broad range of laboratory tests using reactions of blood serum and other bodily fluids. |
| The Serology section of forensic labraotory may deal with any of the following: | -Blood Typing, -Characterization of unknown blood, -stain patterns for crime reconstruction, -paternity testing, -Semen identification in rape cases, DNA techniques used for identificaiton |
| Three questions that must be answered by the forensic investigator when suspected blood stains are found at a crime scene | 1) Is it blood? (Benzidine Test, ***Kastle-Myer test, ***Luminol Test 2) Is it Human blood? (precipitin Test) 3)Can it be associated with an individual? (***DNA Profiling) |
| Luminol Test for blood | Red Blood cells contain hemogoblin and iron. Iron reacts with the ingredients in Luminol which can be made visible with a UV light. |
| Kastle-Myer test for Blood | The Kastle-Myer test uses a chemical reaction between blood and hydrogen peroxide to produce a pink color. |
| Blood Evidence | -Blood (if found at the crime scene) can be valuable in many ways -Tests for blood are so sensitive that they will expose the presence of blood even after a surface has been wiped clean -Blood that is many years old still be classed & analyzed for DNA |
| Blood Typing | -Blood typing is often used to eliminatae suspects -It is cheaper and less time consuming that DNA profiling -There are four blood types (every living person belongs to one of the 4) -Blood typing is considered class evidence |
| Blood typing (2) | A (+ or -) B (+ or -) AB (+ or -) O (+ or -) |
| O positive O negative A positive A negative B positive B negative AB positive AB negative | 35% 13% 30% 8% 2% 2% 1% |
| Blood type Compatibility: If you are O, you can recieve If you are A, you can recieve if you are B, you can recieve if you are AB, you can recieve | O, O- only O- O, A, A- only A- & O- O, B, B- only O- B- AB+ all, AB- all the negatives |
| Blood Spatter as Evidence | Blood spatter, or bloodstain pattern interpretation, is a technique that seeks to piece together the events that caused bleeding. Knowing how blood got on the wall or other surface can be helpful in determining if a crime was committed |
| One of the first things that a forensic investigator needs to do when examining a blood spatter is to ___ that the material is indeed blood. | Verify |
| This can be determined by using ___ that are portable enough to be used right at the scene. | Tests |
| What does a forensic investigator do? | Determines the trajectory of the blood (where the blood came from and how it spread across the surface) |
| By measuring the shape of the bloodstain on a surface, the ____ of movement can be determined. As well, the ____ at which the blood contacted the surface can be approximated. | Direction, Speed |
| Blood drops form different ____ and ____ | Shapes and sizes |
| What does a Blood Spatter analysis do? | Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene. |
| Blood drops as small ____ | Spheres |
| Drops form ___ when hitting a surface due to the cohesion properties of blood. | circles |
| Size depends on the ___ of the blood drop | speed |
| As a general rule, the ____ the energy of the impact (on the source of the blood), the____ the drops are. | Higher, smaller |
| Free-falling blood has a low velocity, leaving ____ drops | Large |
| What is the fastest a free falling blood drop can travel? | 25 ft/sec |
| Blood always travels in the direction of the applied ___ | Force |
| When a wound is inflicted and blood leaves the body, a blood-spatter ____ may be created | Pattern |
| Investigators have been using blood stain interpretation as a means to re-create crime scenes since ____ | 1939 |
| Given blood spstter patterns, it is possible to determine the ____ the blood was traveling, the ___ __ _____ and the ___ __ ____ of the blood. | Direction, angle of impact, point of origin |
| Directionality | Directionality can be determined by analyzing the tail of the bloodstain. |
| What sets the tale? | Tail |
| Passive drop | The absence of a tail indicates that the blood dropped from a 90⁰ angle |
| Blood stains can be classified by the velocity of the impact that sent them flying from a victim. | High, medium, low velocity |
| Faster droplets | smaller droplets in the air |
| The faster the blood droplet is moving on contact with a surface. | the more it will spread out. |
| higher height | faster on contact with surface = wider drop |
| Low Velocity | Passive drops, a punch or stab |
| Medium Velocity | A spatter like a blunt instrument swung by hand |
| High velocity | A mistlike spatter resulted from a gunshot |
| Blood spatter angle | The angle at which a blood drop hits a surface can help determine where a person was when they lost blood. |
| 10 degrees | A long line dripping |
| 30 degrees | A long oval tearlike build |
| 40 degrees | a smaller oval |
| 50 degress | a perfect cirlce |
| The location of the source of blood can be determined if there are at least _ drops of blood spatter. | 2 |
| In order to determine this ___ __ ____, investigators must use a method called __ to find the ___ __ ____ | Point of origin, stringing, area of convergence |
| Once AOC is determined, a quick trigonometry calculation can yield the _____ | Point of origin |
| Step 1 Step 2 Step 3 Step 4 | Find good blood spatter String the blood Determine the Angle of Impact |
| Law of Tangent formula | sin-1(width / length) |
| How to determine point of origin | Investigators use a protractor to pull the strings out to the appropriate angle. |
Created by:
samibun