Forensic Blood-Testing Methods
Forensic blood testing refers to using science or technology when examining blood specimens to assist in the investigation and establishment of facts for evidence in a court of law. Forensic methods can include individual use or any combination of various methods involving chemistry, toxicology or pharmacology. With the use of forensic science, a blood sample as small as 10 centimeters can aid crime scene investigators in solving a murder.
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History
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According to Locard's exchange principle, when two objects come in contact, traces from one will transfer to the other. In many brutal crimes, an offender will leave the scene with traces of the victim's blood on his body or clothing, and in some cases, even leave his own blood at the crime scene. This subsequently leads investigators down the right path to identifying the criminal.
The facts
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In any criminal case requiring forensic blood testing, there are some basic questions that need to be answered. Is it even blood? Whose blood is it? Is it human or animal? Is it male or female? Is the blood connected to anyone related to the location of the crime scene? Can a suspect be identified?
Testing of blood specimens is typically performed in a lab and can offer answers to pressing questions. The time frame for obtaining results can vary drastically; while some information can be revealed immediately, other results can take several months to determine.
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Types
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DNA testing According to "Physical Evidence in Forensic Science" by Dr. Henry C. Lee, a forensics expert who has assisted law enforcement in more than 6,000 major criminal investigations, and Howard Harris, a lawyer and forensic scientist, blood evidence is found most often in crimes of violence such as homicide, assault and sexual assault. Blood specimens can be found in a variety of forms, such as liquid, dried or coagulated, and different testing methods can be performed based on the blood evidence.
Methods can range from use of Luminol, which is sprayed at the crime scene and reacts to blood allowing criminalists to detect blood, to DNA testing.
DNA Testing
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During the past 100 years, forensic science has evolved from the simple determination of identifying blood as human or animal, to the present when DNA comes in to play.
In 1984, Dr. Alec Jeffreys, a researcher at the Lister Institute Leicester University in England, discovered highly repetitive sequences in the genetic code that could be used to identify an individual through a small specimen collection of blood, according to an article in Forensic Focus magazine. This scientific development brought us to the DNA analysis we know today and which has solved numerous criminal cases.
Determinations
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Once the specimen is determined to be blood, the criminalists have more questions to answer. According to The American Chemical Society, blood stains can provide a variety of important clues such as where the crime took place and even a time frame as to when it occurred. The symmetry of blood droplets is important as well, as it can hint to even the smallest details such as from where the blood fell.
Benefits
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By using forensic science to test blood, investigators can locate a variety of clues that can point to the perpetrator in a case. Criminalists and scientists can work together to find blood at a crime scene, and use chemistry based techniques to uncover clues and solve cases.
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References
Resources
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