CSI And Blood Evidence
What is blood made of?
Blood, from a simplistic point of view, is comprised of a liquid and solid. The liquid is known as the plasma. Typically your solids are your blood platelets, your red blood cells, and your white blood cells. From a descriptive point of view, I think that's the best way to envision the composition of blood.
How does the classification of blood type help in CSI?
Blood typing today doesn't help a forensic scientist. It used to, but when DNA analysis came along in the 1980s, it quickly supplanted the traditional blood type ABO test for the analysis of crime scene blood stains. So today, blood typing is more of a historical note than anything else. It is very unusual, probably non existent, to hear of anybody typing blood for its ABO content in a forensic situation.
Why are blood stains studied in CSI?
Blood stains are studied for a number of reasons. Perhaps one important reason is to make a determination as to the DNA composition of the blood stain. Another important purpose of blood stain analysis is that when blood hits an object it forms a pattern and the patterns can be very important in reconstructing what occurred at a crime scene. How many blows an individual was subjected to, or what movement a victim undertook during the commission of a crime or a perpetrator. These are all questions that can be perhaps answered by studying the blood stain patterns that are present at crime scenes.
What must a scientist determine from blood stains in a CSI?
The first thing that we have to do when we examine a blood stain is to make a determination as to whether it is indeed blood, as opposed to ketchup or some other material that may look like blood. Typically, we'll use a color test known as the Castlemeyer color test, to answer that question. However, in some crime scenes, it's just very difficult to find these things. The blood may have been cleaned up thoroughly or there may be just a few specks that are hard to see with the human eye. We use a test known as the luminal test, which is a test that is very sensitive for blood, in order to ascertain whether there are any trace amounts of blood that may be present at a crime scene. Essentially, the luminal test involves spraying a suspect area, darkening the room, and looking for a glow or the emanation of light from the suspect stain. If that occurs, then there's a good chance that we are dealing with blood. If we do have blood, we now have to determine the species of the blood. Is it human, or animal? Here, we rely upon commercial anti-serum. There are companies that forensic scientists can purchase anti-serum related to various animals such as deer, cats, or dogs. Serological tests will be carried out in the laboratory in order to ascertain whether a blood stain emanated from a human or from some other animal using this anti-serum that is commercially available. Finally, once we ascertain that the blood emanated from a human being, then we undertake DNA testing.
What tests are used to study blood stain patterns in CSI?
Blood stain patterns are very important in attempting to reconstruct what happened at a crime scene. These are visual patterns that must be well documented at the crime scene; photographs, notes and all of that. The analysis must be undertaken and it is very important to understand this, by a skilled individual. Somebody who has been schooled in blood stain pattern analysis and has a good deal of practical experience in carrying out these examinations. But these examinations are visual in nature. There are no technological instruments or anything like that that are around, that will allow one to do these kinds of things, other than just looking at the stain with an experienced eye and putting the stain in the context of the entire crime scene.
What is 'blood-stain convergence' and how is it studied in CSI?
Blood-stain convergence is a form of blood-stain pattern analysis, and it allows us to make a determination as to the origin of a stain pattern. Often at crime scenes when there is bleeding, there is a lot of movement; movement on the part of the perpetrator, perhaps even movement on the part of the victim. The convergence protocol procedure allows the blood-stain pattern analyst to ascertain the point of origin or area of origin of a series of blood-stains.
