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CriminalisticsAn Introduction to Forensic Science
CHAPTER
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Crime Scene Reconstruction• The method used to support a likely sequence of
events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident, is referred to as reconstruction.
• Crime-scene reconstruction relies on the combined efforts of medical examiners, criminalists, and law enforcement personnel to recover physical evidence and to sort out the events surrounding the occurrence of a crime.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Crime Scene Reconstruction• A crime-scene investigator can bring special skills to the
reconstruction of events that occurred during the commission of a crime.
• For example, a laser-beam is used to determine the approx. bullet path (trajectory) to help determine the probably position of the shooter relative to the victim.
• The collection, documentation, and interpretation of physical evidence is the foundation of reconstruction.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
FIGURE 4–1 A laser beam is used to determine the search area for the position of a shooter who has fired a bullet through a window and wounded a victim. The bullet path is determined by lining up the victim’s bullet wound with the bullet hole present in the glass pane.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Aurora Colorado Movie Theater Shooting
5
July 20, 2012 – during the midnight showing of The Dark Knight Rises, 24 year old James Holmes, armed with a semi-automatic rifle, shotgun, and .40 caliber Glock handgun fired 76 shots into the crowd. Killing 12 and injuring more than 70.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
General Features of Bloodstain Formation
• Bloodstain patterns deposited on floors, walls, bedding, and other relevant objects can provide valuable insights into events that occurred during the commission of a violent crime.
• The crime scene investigator must remember that the location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the events that produced the bleeding.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
General Bloodstain Features• Bloodstain pattern interpretation may uncover:
The direction from which blood originated The angle at which a blood droplet struck a surface The location or position of a victim at the time a bloody
wound was inflicted The movement of a bleeding individual at the crime
scene The approximate (minimum) number of blows that
struck a bleeding victim The approximate location of an individual delivering
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Directionality and Angle of Impact• The impact angle of blood on a flat surface can be
determined by measuring the degree of circular distortion. At right angles (90 degrees) the blood drop is circular; as the angle decreases, the stain becomes elongated.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Impact Bloodstain Spatter Patterns• Impact spatter occurs when an object impacts a
source of blood. The most common type of bloodstain pattern found at a crime scene. Consist of many drops radiating in direct lines from the origin of blood to the stained surface.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Impact Bloodstain Spatter Patterns• Forward spatter is projected outward and away
from the source. (ie. exit wound) In the same direction as the force.
• Back spatter, also known as blow-back spatter, is projected backward from the source. (ie. entrance wound) Can potentially be deposited on the object or person who created the impact.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Origin of Impact Patterns Area of Convergence
Impact patterns can offer investigators clues about the origin of the blood spatter and the position of the victim at the time of impact.• The area of convergence is the point on a two-
dimensional plane from which the drops in an impact pattern originated.
• This can be established by drawing straight lines through the long axis of several individual bloodstains, following the line of their tails.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
FIGURE 4–7 An illustration of stain convergence on a two-dimensional plane. Convergence represents the area from which the stains emanated.The Institute of Applied Forensic Technology, Ocoee, Florida
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Area of Origin• The area of origin of an impact bloodstain pattern is
the area in a three-dimensional space from which the blood was projected.
• This will show the position of the victim or suspect in space when the stain-producing event took place.
• The string method is commonly used at a crime scene to approximate the position of the area of origin using found angles of impact of individual stains in the pattern.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Back Spatter Depending upon the distance from the victim that the gun was discharged, some back spatter may strike the gunman and enter the gun muzzle. This is called the drawback effect.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Cast-off Spatter• The features of the cast-off pattern are affected by
the size of the object, the amount of blood, and the direction the object was moving.
• Drops from small pointed surface (knife) will be smaller and more linear. Drops from a large or blunt surface (bat, shovel) will be larger and the pattern wide. Less blood on the object will produce smaller stains.
• By counting and pairing forward/backward patterns, one may determine the minimum number of blows delivered.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Arterial Spray Spatter• Arterial spray spatter is caused by an injury to the
heart or a main artery and the of the continuing pumping.
• The site of the initial injury to the artery can be found where the pattern begins with the biggest spurt. The trail away from this point shows the victim’s movement.
• The oxygenated blood spurting from the artery tends to be a brighter red color than blood expelled from impact wounds.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
FIGURE 4–11 Arterial spray spatter found at a crime scene where a victim suffered injury to an artery.Norman Reeves, BPA Consulting, Tucson AZ, www.bloody1.com
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Expirated Blood Patterns• An expirated blood pattern is created by blood that is
expelled from the mouth or nose from an internal injury.
• The presence of bubbles of oxygen in the drying drops or a lighter color as a result of dilution by saliva can differentiate a pattern created by expirated blood.
• The presence of expirated blood gives an important clue as to the injuries suffered and the events that took place at a crime scene.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Other Non-Spatter PatternsNot all bloodstains at a crime scene appear as spatter patterns…..
• A contact or transfer pattern is created when an object with blood on it touches another object that does not have blood on it. (ie. handprints, footprints, shoeprints, fabric impressions in blood)
• Simple transfer patterns are produced when the object makes contact with the surface and is removed without any movement of the object.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
Pools• A pool of blood occurs when blood collects in a level
(not sloped) and undisturbed place. Blood that pools on an absorbent surface may be absorbed (bed or sofa) throughout the surface and diffuse, creating a pattern larger than the original pool.
• Considering the drying time of a blood pool can yield information about the timing of events that accompanied the incident.
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
FIGURE 4–19 The grid method may be used for photographing bloodstain pattern evidence.R. R. Ogle, Jr., Crime Scene Investigation and Reconstruction, 3rd ed., Prentice Hall, Upper Saddle River, N.J., 2011
Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein
FIGURE 4–20 The perimeter ruler method may be used for photographing bloodstain pattern evidence.Courtesy Evident, Union Hall, VA 24176-4025, www.evidentcrimescene.com