Blood Analysis in the Scope of Forensic Science

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In the world of forensic science, there are many fields involved in a crime scene in order to restore the crime scene in hope of finding out the truth of the crime. Among all the samples, we have chosen blood as our main focus in this topic. This is because blood can clearly indicate a person, which means having the information of one’s blood will review much clues or evidence as we cannot change or alter our identities or DNA in our blood.

Professors who analyses blood is categorized as forensic serologists that specialize in body fluids such as blood, semen, and saliva. What are their roles? They mainly work for blood testing, identifying the type and characteristic of blood because every human possesses a unique DNA which is impossible to have replication or duplication. Next, they also examine the blood stain found in the crime scene to give more clues about certain murderer or to identify the identity of the victims. DNA typing and preparation of court testimony and evidence are also part of their jobs.

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Why blood is chosen to be examined or analysis even though the cost for this is high? The reasons being is because blood is the most well-known and significant evidence in the modern criminal justice system. In forensic investigator, blood evidence can link to a suspect which is call as Locard’s Exchange Principle. Next, the uniqueness of a bloodstain patterns is able to reveal a great deal about the position and movement during the crime. Nevertheless, it could manage to destroy self-defense arguments of suspects.

The nature of blood has some general characteristics which are well-known. First of all, talking about the nature of blood, it is a slightly alkaline fluid that made up of 90% of a human weight. Blood circulates throughout our bodies, not only to nourish our cells but also play a vital role in transporting oxygen and waste in and out of our bodies. There are generally two parts in blood which are classified as fluid and non-fluid portion. In the fluid portion, there are existence of plasma and serum whereas red-blood cells are in non-fluid phase. In short, blood is composed of several components such as water, enzymes, cells, protein and other inorganic substances.

When a forensic investigator analyze bloodstain, they will follow these five specific guidelines for determining the nature of a crime. The five guidelines are as follow:

  1. Is the sample blood?
  2. Is the sample animal blood?
  3. If the sample is animal blood, from what species did it come from?
  4. If the sample is human blood, what is the blood type of the blood?
  5. Can the sex, age, and race of the source of blood be determined?

For the first guideline, color or crystalline are used in determine whether a sample is blood or not. The Benzidine test was highly recommended and widely used in the past until it was discovered to be known as carcinogen. Nowadays, investigators implement Kastle-Meyer test to run the investigation which uses the chemical, phenolphthalein, working on the fact that when phenolphthalein comes in contact with hemoglobin, the peroxidase enzymes that are released and cause a bright pink color to appear. Moreover, to enhance the investigation in determining the sample, luminol test are applied. Luminol is a chemical sprayed on carpets or furniture that will reveals a slightly phosphorescent light with the light off where the bloodstain is present. Not only that, Teichman test, the Takayama test as well as Wagenhaar test are used to examine long-dried blood which tends to crystalize or can be crystalize by mixing it with various of saline-acid mixtures.

Secondly, in determining the blood at the crime scene is originated from an animal, forensic investigators use antiserum or gel tests. Why forensic investigators take time and money to determine the sample of animal blood is because any possibility of an injury to the household pet, caused by a perpetrator or another animal, must be eliminated. To determine whether a sample is originated from human or animal, precipitin test is conducted. This test is a process which involves in injecting an animal with human’s blood. In the body of the injected animal, it will create anti-human antibodies automatically, which then extracted from the animal’s serum. If this serum is mixed with the sample collected from the crime scene show clotting, it can be concluded that the blood is human blood.

It is always useful if the sample of blood can allow forensic investigators to estimate the blood owner’s age, sex or even race. Forensic scientist uses various color and nitrate tests and applies heredity principle to the tests. Up-to-date, there are no exact determinations are possible, there is only estimation. However, in determination of age, clotting and crystallization can help to approximate the age. On the other hand, sex hormone such as testosterone and chromosome testing can help to determine sex. For race, certain genetic markers involving protein and enzyme tests can help establish race.

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