Within forensic science, there are two types of characteristics, class and individual. These are forms of physical evidence that become crucial to solving a crime. With the use of new technology, the scientists are able to determine if a known sample of a small fiber, paint chip, or shoe pattern is consistent with the unknown sample found at the scene. When individual characteristics are determined, the suspect has been linked to the scene.
Physical evidence establishes that a crime has been committed, establishes the key elements of the crime, links the scene to the victim, the victim to the suspect, and the suspect to the scene. Besides DNA, the next best evidence would be individual characteristics. But first, the evidence must be classified with class characteristics, which is more general.
Class characteristics are general characteristics that define a category of items or objects, but are not alone sufficient to define individuality. An example would be a shoe print in the dirt. The print is lifted for comparison. There are hundreds of different shoes in the world, with hundreds of different sole patterns. Class characteristics allow the scientists to narrow the pattern down to specific shoes. The FBI has created a shoe and tire database for such purposes. Once the laboratory has narrowed the pattern to one shoe pattern, they are able to address the issue of whether or not it was the print found at the crime scene.
Individual characteristics are exceptional characteristics that may establish the uniqueness of an object. These unique markings are accidental, or unintentional, characteristics resulting of wear and random markings on the item during manufacturing. The way in which a person walks creates a wear pattern that is unique only to them on the soles of their shoes, along with normal wear of the shoes. This is what the scientists look for when doing a comparison. Scientists are matching up the individual characteristics of the known sample (suspect’s shoe) and unknown sample (print at the crime scene).
With such evidence, the scientists are able to state that the suspect’s shoe was without a doubt, the shoe that was found at the crime scene. This places the suspect at the scene, which is what is needed to prove that the suspect could have committed the crime. Class and individual characteristics can also be found in fingerprints, on a spent bullet, a prying tool, and tread patterns of an automobile.
Friday, March 27, 2009
Friday, March 20, 2009
Outside the Lab
When one thinks of Forensic Science, the lab comes to mind. What if I told you that Forensic Science could be applied outside of the lab? It is all part of the criminal investigation process and the reconstruction of the crime scene. The evidence found at the crime scene tells a story that allows Forensic Investigators to reconstruct how the crime occurred.
Reconstruction is the formulation of a best theory of a set of events, based on the consideration of all the available evidence and information. In order to reconstruct the crime scene the sequence of events must be understood. Patterns help to establish one’s understanding: blood patterns, glass fracture patterns, track and trail patterns, gunshot residue patterns, trajectory patterns, fire burn patterns, and modus operandi.
Blood makes a predictable pattern due to its make-up, viscosity, density and other physical properties when it exits the body: low, medium, and high velocity. Low velocity is created only by the pull of gravity; if the person is stationary than the blood will pool; if the person is moving, the blood droplets could tell investigators the direction the person was moving. Medium velocity blood droplets are smaller than low velocity and more numerous: approximately 4 mm in diameter. These droplets occur when an object hits pooled blood. High velocity droplets are even smaller than medium velocity and more numerous: approximately 1 mm in diameter to fine mist. This pattern is typical of gunshot wounds and explosions. Blood spatter pattern is the most common type of reconstruction pattern.
Gunshot residue patterns allow investigators to determine the distance of the shooter. When a firearm is discharged, the force of expanding gases disperses materials from the firearm. Depending on the distance, different characteristics will appear. If the wound is a contact wound, one will see blast destruction such as tearing of the clothes or skin and soot and powder inside the garment or the wound. As the shooter moves further away, then the appearance of soot (smudging) around the wound becomes less dense; tattooing on the skin, which are powder particles embedded in and under the skin, begin to loosely adhere to the surface the further the distance.
Because of these predictable patterns, Forensic Investigators can predict the sequence of events while at the scene. Such patterns could also lead to the body if one was not found at the primary scene. To be thorough, the Investigators will perform experiments in the lab to give corroborative evidence: physical evidence that differs from but strengthens or confirms other evidence.
Reconstruction is the formulation of a best theory of a set of events, based on the consideration of all the available evidence and information. In order to reconstruct the crime scene the sequence of events must be understood. Patterns help to establish one’s understanding: blood patterns, glass fracture patterns, track and trail patterns, gunshot residue patterns, trajectory patterns, fire burn patterns, and modus operandi.
Blood makes a predictable pattern due to its make-up, viscosity, density and other physical properties when it exits the body: low, medium, and high velocity. Low velocity is created only by the pull of gravity; if the person is stationary than the blood will pool; if the person is moving, the blood droplets could tell investigators the direction the person was moving. Medium velocity blood droplets are smaller than low velocity and more numerous: approximately 4 mm in diameter. These droplets occur when an object hits pooled blood. High velocity droplets are even smaller than medium velocity and more numerous: approximately 1 mm in diameter to fine mist. This pattern is typical of gunshot wounds and explosions. Blood spatter pattern is the most common type of reconstruction pattern.
Gunshot residue patterns allow investigators to determine the distance of the shooter. When a firearm is discharged, the force of expanding gases disperses materials from the firearm. Depending on the distance, different characteristics will appear. If the wound is a contact wound, one will see blast destruction such as tearing of the clothes or skin and soot and powder inside the garment or the wound. As the shooter moves further away, then the appearance of soot (smudging) around the wound becomes less dense; tattooing on the skin, which are powder particles embedded in and under the skin, begin to loosely adhere to the surface the further the distance.
Because of these predictable patterns, Forensic Investigators can predict the sequence of events while at the scene. Such patterns could also lead to the body if one was not found at the primary scene. To be thorough, the Investigators will perform experiments in the lab to give corroborative evidence: physical evidence that differs from but strengthens or confirms other evidence.
Thursday, March 5, 2009
DNA
Video Link: https://www.findthemissing.org/how_it_works_video/NamusVideo640.htm
DNA has become an important piece in how society views forensic science. Again, due to popular culture, it is believed that every case must have DNA present; if a jury does not hear DNA evidence presented in court, the suspect may go free because the case was not solid without DNA evidence. DNA, in addition to gaining a conviction, can identify a missing person, deceased or alive. The Criminal Justice System utilizes DNA to its advantage.
DNA is the abbreviation for deoxyribonucleic acid, and is the fundamental building block for all living organisms (DNA Initiative). With the exception of identical twins, each person’s DNA is unique. DNA is a powerful tool for the Criminal Justice System. In combination with Locard’s Principle, a suspect will leave something at crime scene and take something away, DNA can link a suspect to the victim, victim to the suspect, and both to the crime scene. All that is needed is blood, bone, hair, or other body tissues and products.
Even with the smallest piece of DNA, the forensic laboratory can now create a profile of the perpetrator or missing person. The profile is formally called DNA fingerprinting or DNA typing (DNA Initiative). With the unknown sample from a scene and a known sample from the suspect, the laboratory can compare the two and either confirm suspicions or exclude an individual. Usually a range is given: the suspect’s DNA matches the unknown sample by 1:1.5 billion. This proves that the suspect is the only one who could have committed the crime, or the decomposed body is that of the missing girl.
In addition, to help solve cold cases or to exonerate those of innocence, a DNA database has been created. These databases are found at local, State, and national levels. Individuals convicted of felonious crimes must submit a DNA sample. The sample is entered in CODIS (Combined DNA Index System) where it will remain for any further crimes that an individual may commit (DNA Initiative).
http://www.dna.gov/
DNA has become an important piece in how society views forensic science. Again, due to popular culture, it is believed that every case must have DNA present; if a jury does not hear DNA evidence presented in court, the suspect may go free because the case was not solid without DNA evidence. DNA, in addition to gaining a conviction, can identify a missing person, deceased or alive. The Criminal Justice System utilizes DNA to its advantage.
DNA is the abbreviation for deoxyribonucleic acid, and is the fundamental building block for all living organisms (DNA Initiative). With the exception of identical twins, each person’s DNA is unique. DNA is a powerful tool for the Criminal Justice System. In combination with Locard’s Principle, a suspect will leave something at crime scene and take something away, DNA can link a suspect to the victim, victim to the suspect, and both to the crime scene. All that is needed is blood, bone, hair, or other body tissues and products.
Even with the smallest piece of DNA, the forensic laboratory can now create a profile of the perpetrator or missing person. The profile is formally called DNA fingerprinting or DNA typing (DNA Initiative). With the unknown sample from a scene and a known sample from the suspect, the laboratory can compare the two and either confirm suspicions or exclude an individual. Usually a range is given: the suspect’s DNA matches the unknown sample by 1:1.5 billion. This proves that the suspect is the only one who could have committed the crime, or the decomposed body is that of the missing girl.
In addition, to help solve cold cases or to exonerate those of innocence, a DNA database has been created. These databases are found at local, State, and national levels. Individuals convicted of felonious crimes must submit a DNA sample. The sample is entered in CODIS (Combined DNA Index System) where it will remain for any further crimes that an individual may commit (DNA Initiative).
http://www.dna.gov/
Subscribe to:
Posts (Atom)