chapter 4 crime scene reconstruction spring 2017

CriminalisticsAn Introduction to Forensic Science

CHAPTER

Criminalistics: An Introduction to Forensic Science, 11eRichard Saferstein

Copyright © 2015 by Pearson Education, Inc.All Rights Reserved

ELEVENTH EDITION

Crime Scene Reconstruction: Forensic Bloodstain Pattern Analysis

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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.



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.

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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.

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Aurora Colorado Movie Theater Shooting

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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.




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Laser Bullet Trajectory Reconstruction was done on all the shots fired.




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Shooting Victims



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.



General Features of Bloodstain Formation

• Controlled experiments using surface materials comparable to those found at the crime scene can assist with the interpretation.



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

blows that produced a bloodstain pattern



Effects of Surface Texture• Surface texture and the stain’s shape, size, and location

must be considered when determining a bloodstain’s direction, dropping distance, and angle of impact.

• Surface texture is of paramount importance. Comparisons between standards and unknowns are valid only when identical surfaces are used.

• In general, the harder and less porous the surface (ie. glass or smooth tile), the less spatter results.

• Rough surfaces (ie. concrete floor or wood) usually result in irregularly shaped stains w/serrated edges, possibly with satellite spatter.



Blood Drop Off A Pipette



Blood Drop 10cm Onto Cardboard



Blood Drop 10cm Onto Carpet



FIGURE 4–2b A bloodstain from a single drop of blood that struck a cotton muslin sheet after falling 24 inches.By A.Y. Wonder

Irregular shapeSatellite spatter present



Directionality and Angle of Impact• The direction of travel of blood striking an object may

be discerned because the pointed end of a bloodstain always faces its direction of travel.



Angle of Impact Blood At 20 Degrees –Side View



Angle of Impact Blood At 20 Degrees –Front View



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.



Directionality and Angle of Impact• Mathematically, the angle of impact can be

calculated by the equation and determining the inverse of Sine A:

Width of blood stainSin A = -----------------------------

Length of blood stain



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.



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.



Classifying Impact Spatter• Using droplet size to classify impact patterns by velocity

gives investigators insight into the general nature of a crime but cannot illuminate the specific events that produced the spatter pattern.

Low Velocity Spatter:• Drops with diameters of 4 mm or more normally

produced by an applied force of up to 5 ft/sec.• Normally produced by gravity alone.

In general, as the force and velocity increase, the Diameter of the resulting blood drop decreases.



Classifying Impact Spatter Medium Velocity Spatter:

• Drops with diameters from 1-4 mm with an applied force of 5 to 25 ft/sec.

• Normally associated with blunt force trauma.



Classifying Impact Spatter High Velocity Spatter:

• Very fine drops with diameters of less than 1 mm from an applied force of 100 ft/sec or faster.

• Gunshot exit wounds or explosions.



Classifying Impact Spatter• Using droplet size to classify impact patterns is a

useful tool in giving insight to the general nature of the crime.

• HOWEVER, they cannot give you specific events or mechanisms as to how that stain pattern was produced.

• One should use stain size categories very cautiously and for descriptive purposes only in evaluating impact spatter patterns.



FIGURE 4–6a The action associated with producing impact spatter. By A.Y. Wonder

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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.

Can only be done on drops with directionality



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



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.



More Bloodstain Spatter Patterns• Gunshot spatter is fine forward spatter from an exit

wound and back spatter from an entrance wound. However, the gunshot produces only back spatter if the bullet does not exit the body.

• The presence of back spatterin the weapon’s muzzle is consistent with the weapon’s having been close to the victim at the time of firing.



Fatal Gunshot Wound



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.



Cast-off Spatter• A cast-off pattern is created when a blood-covered

object flings blood in an arc onto a nearby surface.

• This kind of pattern commonly produced by a bloody fist or weapon between delivering blows.



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.



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.

• By counting and pairing forward/backward patterns, one may determine the minimum number of blows delivered.



FIGURE 4–6b The action associated with producing cast-off spatter.By A.Y. Wonder

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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.



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



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.



Expirated Blood Patterns



Void Patterns• A void is created when an object blocks the

deposition of blood spatter onto a target surface or object and the spatter is deposited onto the object or person instead.

• The blank space on the surface or object may give a clue as to the size and shape of the missing object or person.

• Voids may be applicable for establishing the body position of the victim or assailant at the time of the incident.



Void Pattern



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.



Contact/Transfer Patterns• The size and general shape of the object may be seen in a

simple transfer.

• Other transfers known as swipe patterns may be caused by movement of the bloody object across a surface.

• Initial contact point will be darker and will lighten and feather as the pattern moves away from initial contact point.



Blood Swipe Across Plexiglass



Flow Patterns• Flow patterns are made by drops or large amounts of

blood flowing by the pull of gravity.

• The flow direction may show movements of objects or bodies while the flow was still in progress or after the blood dried.

• Interruption of a flow pattern may indicate the sequence and passage of time between the flow and its interruption.



Flow Patterns



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.

• Dependent on environmental conditions.



Pools• Nicole Brown Simpson crime scene.



Skeletonization• The phenomenon of skeletonization occurs when the

edges of a stain dry to the surface.

• This usually occurs within 50 seconds of deposition of droplets, and longer for larger volumes of blood.

• After this time, if the bloodstain is altered by a contact of wiping motion, the skeletonized perimeter will be left intact.

• Knowing the skeletonization time, an investigator determine the timing of movement or activity.



Skeletonization



Drip Trail Patterns

• A drip trail pattern is a series of drops that are separate from other patterns, formed by blood dripping off an object or injury.

• The stains form a kind of line or path usually made by the suspect after injuring or killing the victim or injuring themselves.

• The pattern may show direction and speed of movement, lead to a discarded weapon, or provide identification of the suspect by his or her own blood.



Drip Trail Patterns



Bloodspatter 101



Documenting Bloodstain Evidence• Investigators should note, study, and photograph

each pattern and drop to accurately record the location of specific patterns and to distinguish the stains from which laboratory samples were taken.

• The photographs and sketches should also point out specific stains used to determine direction of force, angle of impact, and area of origin.



Documenting Bloodstain Evidence• Two techniques used to document bloodstain patterns

are: Grid method

• A grid of squares of known dimensions are set up over the entire pattern.

Perimeter ruler method• A rectangular border of rulers is set up around each

pattern and a smaller ruler next to each stain.

**With both methods photograph overall, mid-range and close-ups of pattern and stains.



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



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



Interpreting Bloodstain Evidence• Some jurisdictions have a specialist on staff who will

decipher patterns either at the scene or from photographs at the lab.

• However, it is important that all personnel be familiar with patterns to properly record and document them for use in reconstruction.



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