Crime-Scene Reconstruction: Bloodstain Pattern Analysis PDF

Criminalistics: An Introduction to Forensic Science Twelfth Edition Chapter 4 Crime-Scene Reconstruction: Bloodstain Pattern Analysis Copyright © 20...

Criminalistics: An Introduction to Forensic Science Twelfth Edition Chapter 4 Crime-Scene Reconstruction: Bloodstain Pattern Analysis Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Crime Scene Reconstruction Crime-scene Reconstruction = method used to support a likely sequence of events – By the observation and evaluation of physical evidence, and – By statements made by those involved with the incident – relies on the combined efforts of medical examiners, criminalists, and law enforcement personnel (to recover physical evidence) Example: a laser-beam is used to determine the position of a shooter who has fired a bullet through a window and wounded a victim. FIGURE Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights 4–1 Reserved  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 number of blows that struck a bleeding victim – The approximate location of an individual delivering blows that produced a bloodstain pattern Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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: – harder and less porous surface(ex: glass or smooth tiles), results in less spatter results. – Rough surfaces (ex: concrete floor or wood), results in irregularly shapes stain with satellite spatter FIGURE 4–2a A bloodstain from a single drop of FIGURE 4–2b A bloodstain from a single drop of blood blood that struck a glass surface after falling 24 that struck a cotton muslin sheet after falling 24 inches. inches. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved How Surface Texture Affects Bloodstain Patterns https://youtu.be/3fqz4qWqaX0?t=119 Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Directionality and Angle of Impact The direction of travel of blood striking an object may be discerned à the pointed end of a bloodstain always faces its direction of travel. The impact angle (A) of blood on a flat surface can be determined by measuring the degree of circular distortion. – At right angles the blood drop is circular; – as the angle decreases, the stain becomes elongated. – can be calculated by determining the inverse of Sine A: Figure 4–4 a single drop of human blood that fell 24 inches and struck hard, smooth cardboard Ø Top drop at 50 degrees àthe collection of blood shows the direction. Ø Lower drop at 15 degrees. à the tail shows the direction. Figure 4–3 A bloodstain pattern produced by drops of blood that were traveling from left to right. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved How Impact Angle Affects Bloodstain Elongation https://youtu.be/8BaJwG94jQg?t=24 Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Impact Bloodstain Spatter Patterns 1. Impact spatter occurs when an object impacts a source of blood. 2. Forward spatter is projected outward and away from the source. 3. Back spatter, also known as “blow-back spatter”, is projected backward from the source. Figure 4–5 Impact spatter produced by an automatic weapon. The arrows shows multiple direction of travel for skull fragments emanating from the gunshot. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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 à Drops with diameters of 4 mm or more normally produced by an applied force of up to 5 ft/sec. – Medium Velocity Spatter à Drops with diameters from 1-4 mm with an applied force of 5 to 25 ft/sec. – High Velocity Spatter à Drops with diameters of less than 1 mm from an applied force of 100 ft/sec or faster. The classifications of impact spatter as low, medium, and high velocity cannot illuminate the specific events that produced the stain size pattern. In general, one should use stain size categories very cautiously and for descriptive purposes only in evaluating impact spatter patterns. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Sources of Blood Spatter Action associated with producing a spatter 1. Impact Spatter 2. Cast- Off Spatter 3. Arterial Spray Spatter FIGURE 4–6a FIGURE 4–6b FIGURE 4–6c The action associated with The action associated with The action associated with producing impact spatter. producing cast-off spatter. producing arterial spurt spatter. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Area of Convergence 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. FIGURE 4–7: An illustration of stain convergence on a two-dimensional plane. Convergence represents the area from which the stains emanated. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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. Figure 4–8 An illustration of the string method used at a crime scene to determine the area of origin of impact blood spatter. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Blood Stain Analysis: Calculating the Area of Convergence and Origin http://www.YouTube.com/watch?v=3jFKZaSeNjg https://youtu.be/3jFKZaSeNjg Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Gunshot Spatter 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. 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. Figure 4–9 An impact spatter pattern emanating from a bullet striking a blood source (in this case a sponge) before passing through a cardboard target. Mist comes from the muzzle blast, not from the bullet impacting the blood source. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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. 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 4–10 Swing was upper right to lower left. Return to position for the next blow was short swing at left. Cast offs depend entirely on the weapon’s ability to acquire and hold blood, how the swing is achieved, and where in space the victim is located for the blows to be struck. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Arterial Spray Spatter Arterial spray spatter is caused by an injury to the heart or a main artery and the pressure 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. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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 Figure 4–12 An example of blood expelled with two wheezes from the mouth. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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. Figure 4–13 A void pattern is found behind the door where the surface of the door blocked the deposition of spatter on that area. This void, and the presence of spatter on the door, shows that the door was open when the spatter was deposited. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Contact/Transfer Patterns A contact or transfer pattern is created when an object with blood on it touches one that does not have blood on it. Simple transfer patterns are produced when the object makes contact with the surface and is removed without any movement of the object. 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. Figure 4–14 A transfer pattern consisting FIGURE 4–15: A series of swipe of bloody fingerprints with apparent ridge patterns moving from right to left. detail. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Flows 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. Figure 4–16 The flow pattern suggests that the victim was upright and then fell while blood flowed. The assailant claimed the victim was stabbed while sleeping. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved 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 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. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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. Figure 4–17 Skeletonization is shown in a bloodstain that was disturbed after the edges had time to skeletonize. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Drop Trail Patterns A drop 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. Figure 4–18 A drip trail pattern leads away from the center of the mixed bloodstain pattern. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  Documenting Bloodstain Evidence Investigators should – note, study, and photograph each pattern and drop – accurately record the location of specific patterns – distinguish the stains from which laboratory samples were taken. 2 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. FIGURE 4–20: The FIGURE 4–19 The perimeter ruler method grid method may be may be used for used for photographing photographing bloodstain bloodstain pattern pattern evidence. evidence. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved  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. Copyright © 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved