chapter 11 bloodstain pattern documentation and analysis n.
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  2. Bloodstain Pattern Expert Education and Training • A BPE may have experience as a sworn peace officer, forensic technician or have formal education in the physical sciences or medicine. • All BPEs must receive specialized training & continuing education & crime scene experience & a mentorship, working with a seasoned expert, to be successful in BPA.

  3. Bloodstain Pattern Expert Education and Training (continued) • Practical field experience usually begins with attending a BPA course with lab experiments that allow the student to learn the dynamics & mechanics of bloodstain pattern creation. • Advanced training and a practicum are recommended also. • BPEs should attend seminars & conferences relevant to BPA. • No amount of education or training can replace a BPE mentor with extensive crime scene blood pattern experience.

  4. Blood constitutes approximately 8% of the total body weight of human beings. Blood’s viscosity (resistance to flow) ranges between 4.4 - 4.7. In comparison, water’s viscosity is one. Therefore, blood is nearly five times less resistant to flow than water. Blood possesses adhesive qualities & may transfer & adhere to surfaces it contacts. The size & volume of a blood droplet is dependent upon the object from which the droplet is released. An open, dripping wound will release droplets of a different volume than blood dripping from a weapon. A droplet forming on a large surface will cover more surface area & possess more surface tension, resulting in higher blood droplet volume than a droplet that forms on a small surface. Properties of Blood – Drops and In-Flight

  5. Free-falling blood droplets due to gravity average 4.56mm in size (while in the air) and are .05ml (milliliters) by volume. As a blood droplet descends, the diameter increases as the distance it falls increases because the droplet travels faster as it falls. The droplet will reach a maximum diameter, regardless of the distance or height. The maximum blood droplet diameter occurs when terminal velocity is reached. At this point, gravity & air resistance are balanced so the droplet falls at a constant rate. At a crime scene, the distance a blood droplet fell cannot be determined because the volume of the blood drop is not known. Blood droplets fragment upon impact with a surface. If two blood droplets of different sizes travel at the same speed, the larger drop possesses the capacity to travel farther because it has greater mass & can overcome air resistance easier than the smaller blood droplet. When a blood droplet descends at a 90 degree to a surface, the resulting bloodstain is circular & symmetrical. As a blood droplet impacts a surface from an acute angle, the droplet first contacts the surface, then continues to travel along the surface, often forming a tear-shaped stain. Properties of Blood – Drops and In-Flight

  6. Directionality of Blood Drops • The irregularly-shaped end (jagged or tear drop shape) of a blood drop stain indicates the direction the blood was traveling at time of impact with the surface. • The surface (asphalt, concrete, brick, wood) may distort the entire blood drop stain. • Still, directionality may be determined, depending on the overall appearance of the blood drop stain. • Determining directionality assists with reconstructing movement within the scene & following blood trails throughout & away from the scene.

  7. Impact patterns were originally classified based on the velocity of the droplet upon impact. Low velocity impact pattern - force of 5-ft per second hits a blood source creating a converging pattern of blood drops; majority of the stains 4mm in diameter or larger. Medium velocity impact pattern - force of up to 25-ft per second hits a blood source creating a converging pattern of blood drops; majority of the stains 1 to 3mm or smaller in diameter, with additional drops larger and smaller. High velocity impact pattern - force of 100-ft per second or greater hits a blood source creating a converging pattern of blood drops; majority of the stains less than 1mm in diameter; some mist droplets (those .1 mm or smaller in diameter) may be present; Pattern associated with gunshot wounds. Classifying impact patterns simply as low, medium, or high velocity is often problematic because appearances can be deceiving. Example: a bloodstain pattern may appear to be caused by a high velocity impact, and may be interpreted as a pattern caused by a gunshot when it was in fact blunt force trauma. Pattern Recognition and Classification

  8. Pattern appears to be a high velocity impact, but is not.

  9. Pattern Recognition and Classification • A more holistic & generally accepted bloodstain pattern classification approach analyzes patterns based on physical features of stain size, shape, location, concentration & distribution. • The modern approach classifies bloodstain pattern stains into 3 main categories: • 1) Passive • 2) Spatter • 3) Altered • Subcategories are contained within each main category.

  10. Passive Bloodstain Patterns • A passive bloodstain pattern is affected by gravity & secondary contact with blood at the crime scene. • Patterns affected by gravity include: • drops, blood flow & large volume of blood. • Patterns affected by secondary contact include: • those caused when an object or person contacts blood & transfers it to another object or surface.

  11. Passive Bloodstain Patterns –Transfer Patterns • A transfer bloodstain patternmay be a non-motion or a motion stain pattern; • Individual characteristics may be present in the pattern.

  12. Passive Bloodstain Patterns –Transfer Patterns • Motion transfer patterns are indicative of movement within the crime scene; • may provide clues regarding: • movement of the victim, • attempts to clean the crime scene, • struggles within the scene & other valuable criminal event information. • A motion transfer pattern may be caused by a blood wipe, which occurs when a clean object moves against a bloody surface (e.g., a hand or cloth moving through a pool of blood).

  13. Passive Bloodstain Patterns –Transfer Patterns • A motion transfer pattern may be caused by a blood swipe, which occurs when a bloody object moves along a clean surface (e.g., bloody hair or hand moving across a clean wall or floor).

  14. Passive Bloodstain Patterns –Blood Drops • If the perpetrator was injured & bled, drops of blood may be observed on or around the victim. • A trail of blood may depict the perpetrator’s movements & lead away from the crime scene. • Photo, document & collect all blood drop stains within the scene.

  15. Passive Bloodstain Patterns –Blood Dripping Into Blood • If a person bleeding from an open wound is stationary for a period of time, drops of blood will fall onto a surface area. • As each drop impacts the surface, the blood gathers into a pool. • Each subsequent drop of blood adds to the pool. • As drops land in the pool of blood, tiny fragments of the each drop may break away & land outside the pool. • These tiny fragments of blood are referred to as satellite spatter.

  16. A blood flow pattern is created when a large volume of accumulated blood flows from one area to another based on gravity and the contour of the surface. A flow pattern may be observed on a vertical surface or on a victim’s body as blood flows downward along the contour of the body. If body was moved after blood flow began, a blood flow may be contradictory to gravity. Alarge volume patternis indicative of extensive bleeding in a fixed position. A large volume of blood will pool on a non-absorbent surface and saturate an absorbent surface. If the volume of blood is large enough, blood can penetrate carpet, carpet padding, or several layers of bedding. Passive Bloodstain Patterns –Large Volume & Flow Patterns

  17. Passive Bloodstain Patterns –Large Volume & Flow Patterns

  18. Spatter Bloodstain Patterns • A spatter bloodstain pattern results when blood is placed in flight because of action upon it. • Actions that may create spatter bloodstain patterns include: • Gunshots, • Beatings, • Stabbings, • Satellite (secondary mechanism) spatter, • Projection mechanisms (cast-off patterns from blood, object in motion), & • Arterial and expirated blood (blood forced from a live human body through arterial pressure or coughing action).

  19. Spatter Bloodstain Patterns –Impact Mechanism • An impact mechanism bloodstain patternis created when an action such as blunt force or a gunshot fragments a blood source (victim), creating a converging pattern of individual blood spatter on nearby surfaces. • The size & distribution of spatter within the impact pattern is dependant upon the volume of blood impacted & velocity and mass of the force. • The BPE analyzes the overall pattern as well as individual spatters within the pattern.

  20. Spatter Bloodstain Patterns –Impact Mechanism Gunshot bloodstain patterns typically appear cone shaped. • Individual spatter consists of very fine drops of blood, which are mist-like in appearance. • Medium & large-sized drops of spatter may be observed within the pattern also. • Mist-sized spatter is most indicative of a gunshot because of the high velocity required to fragment blood into very small particles. • The higher the velocity of the bullet, the greater it’s impact and blood fragmentation. • Injuries resulting from power tools and motor vehicle collisions fragment blood into a mist-like spatter also. • Though uncommon, a backspatter pattern may be observed as well.

  21. Spatter Bloodstain Patterns –Impact Mechanism Beating (blunt force) mechanisms generate the largest amount of individual spatter. • Weapons include hammers, bricks, baseball bats, golf clubs, pipes, wrenches & other blunt objects. • Spatter pattern typically radiates from the impact site, which is indicative of the direction of the blood spatter blow. • The distribution & size of impact spatter is dependant upon: • shape and size of the weapon, • amount of force, • direction of the force, • amount of blood available at the wound site, • movements of the victim & perpetrator during the attack.

  22. Spatter Bloodstain Patterns –Impact Mechanism Stabbing Bloodstain Patterns - the bloodstain pattern created depends upon force applied to an open blood source. • With each thrust of the edged weapon, the perpetrator’s fist & weapon impact the blood source, resulting in an impact spatter pattern. • Since the mass of the edged weapon and perpetrator’s fist are often not as large as many blunt force weapons, the resulting edged weapon impact bloodstain pattern is usually smaller in overall pattern size.

  23. Spatter Bloodstain Patterns –Secondary Mechanism Spatter • A satellite spatter is named a secondary mechanism spatterbecause it is produced by a second impact. • Satellite spatter is noted for what it is: a fragmented portion of an original drop of blood.

  24. Spatter Bloodstain Patterns –Projection Mechanism • Aprojection mechanism bloodstain patternis created by blood placed in flight & projected by a force other than an impact. • Cast-off bloodstain pattern - created when blood is dislodged from a bloody object or weapon as it is being swung. • Pattern can be linear or arc-shaped, with individual blood spatters parallel to each other, or teardrop-shaped, indicating directionality of the swing. • Patterns are found in beating & stabbing scenes with stains often located on a ceiling, wall, or floor. • Stains are typically 4–8 mm but may be larger or smaller in size. • A cessation cast-off pattern occurs when a bloody object or weapon strikes another object or surface and comes to a complete stop.

  25. Multiple cast-off patterns from police dog bite on an armed robbery suspect.

  26. Spatter Bloodstain Patterns –Projection Mechanism Arterial bloodstain pattern - created when blood under pressure from a punctured artery of a live person is cast onto a surface. • More severe the damage to the artery, the more blood volume discharged from the artery. • Injury can result from: sharp instrument, blunt force, or gunshot wound. • In some natural death cases, the decedent’s vein may rupture and release blood, creating a bloodstain pattern that appears arterial in nature.

  27. Spatter Bloodstain Patterns –Projection Mechanism Expirated bloodstain pattern - created when a victim coughs, sneezes, or expels blood from of the mouth. • May be associated with a homicide or natural death.

  28. Altered Bloodstain Patterns Clotted Blood - As blood dries, oxygen is expelled from the red blood cells, resulting in a color change to the blood. • When blood is exposed to direct sunlight, it darkens. • As a bloodstain ages, its color change progresses from red to reddish brown, green, dark brown & black. • Drying time for blood varies on: volume of blood, temperature, humidity, air flow & target surface. • As blood clots, the liquid portion of blood (serum) & platelets & fibrinogen separate. • With normal, healthy individuals, time between bloodshed & clotting is 3-15 minutes.

  29. Altered Bloodstain Patterns Diluted blood is usually light brown in appearance, with a darker coloration around the rim & a lighter coloration in the center of the stain. • Diluted blood on clothing may be the result of perspiration or urine mixed with blood. • Blood diluted with saliva can result from expiration. • Head trauma may cause spinal fluid to dilute blood.

  30. Diffused Blood Blood diffusion (separation) is frequently observed when a high volume of blood stains & saturates bedding and clothing. As blood is absorbed by the fabric, the outer edges of the stain appear lighter & less concentrated than the center of the stain. Insect activity in or on blood can distort bloodstain pattern appearance. Fly activity within a bloody crime scene can produce tiny stains, often referred to as fly specks, that may be misinterpreted as spatter stains. Cockroaches & similar insects crawl through blood and leave transfer stains. Altered Bloodstain Patterns

  31. Altered Bloodstain Patterns • Sequenced bloodstain pattern - one of several overlapping bloodstains frequently located at crime scenes. • A determination must be made regarding the sequence of the stain patterns.

  32. Altered Bloodstain Patterns • Some bloodstains are deposited & begin to dry within a few minutes. • Drying may cause the blood to flake, revealing an outline of the original pattern. • Motion through the original, partially dried blood may occur as well, leaving the original outline plus the motion transfer (wipe) at the scene. • The outline of the original stain is referred as a skeletonized bloodstain.

  33. Altered Bloodstain Patterns Void bloodstain pattern - occurs when an object containing a portion of the bloodstain is removed leaving an outline of the voided pattern behind. • The outline lacks blood spatter within the area once occupied by the object. • Can also be caused by victim or perpetrator blocking the blood spatter from hitting a target surface. • An abrupt end to a blood spatter pattern is referred to as a demarcation line.

  34. Photo & document all bloodstain patterns within the crime scene prior to reconstruction of impact mechanism patterns. This ensures a record for subsequent analyses by other BPEs. Photographic Documentation: 1) Overall photos are taken of the entire crime scene, including overall views of the bloodstain patterns within the scene. 2) If multiple bloodstain patterns cover a large surface area (e.g., wall, floor, ceiling), the area can be subdivided into zones or a grid (pre-determined size squares. Place a label (letter/number) & scale in each grid. 3) Take overall photos of the entire surface area, followed by orientation photos of each square within the surface area. 4) Measuring devices illustrating vertical & horizontal distances from the base and side of the affected are set into place so the location of the square is observed in the photograph. Documenting andReconstructing Bloodstain Patterns

  35. 5) Take close-up photos of each square with the measuring device in place. The face of the camera lens must be parallel to the bloodstain pattern. Wide angle should not be used because it distorts the image; A normal lens (50mm) or macro views should be used for all close-up photographs. Non-motion transfer pattern photos: Assigned an evidence number; Take orientation & close-up photos with a scale in place. Camera lens parallel to the evidence & the photo frame is filled with the pattern. Motion transfer patterns photos: Assigned an evidence number; Place a measuring tape or an adhesive-backed ruler along the entire length of the pattern. Photo overall views and photo sections of the pattern. Close-up sectional views - camera lens parallel to the evidence & photo frame is filled with the pattern. Documenting andReconstructing Bloodstain Patterns

  36. Cast-off pattern photos: Similar to lengthy motion transfer patterns & tire impressions, cast-off patterns must to be photo’d in increments. An adhesive-backed ruler is placed along the entire pattern. If the pattern is arc-shaped, the ruler may be cut into sections to curve with the pattern. Photo an overall view with ruler in place & orientation views of pattern in relationship to the rest of the crime scene. Camera on a tripod with face of the camera lens parallel to the pattern; With the ruler in place, take overlapping photos in 1-ft increments until entire pattern is photo’d. Photos should overlap by one-inch to ensure that every portion of the pattern is photographed. Documenting andReconstructing Bloodstain Patterns

  37. Close-up Photography of Impact Mechanism Patterns • Close-up photos must be precise so BPEs can analyze & reconstruct the pattern from the photos. • Many BPEs process digital photos of impact patterns using bloodstain pattern analysis software; • If close-up images are photo’d in RAW format only, the software processing time is slowed considerably. • However, some agencies require forensic technicians to digitally photograph evidence in the RAW format. • If pattern is located on a wall, adhesive-backed rulers are strung from the floor and an adjacent wall across the entire impact pattern; • The rulers are placed from at least two directions (up/down and right/left) across the pattern; • An overall photograph of the impact pattern is obtained and orientation photos of the surrounding area are taken. • Next, close-up photos of the pattern are taken…

  38. Roadmapping Technique: 1) Small scales are labeled with numbers or letters & strategically placed throughout the pattern. 2) If the bloodstain pattern is on a vertical surface such as a wall, a level line is drawn under the scale and blood spatter. 3) Orientation photos of the pattern are taken, including several photos of the scales in the same photograph. Scales are overlapped in subsequent photographs so an orientation to the overall pattern can be created. 4) Close-up photos of the scale and selected bloodstains are taken. Camera must be on a quadripod or tripod & level, with the face of the camera lens parallel to the bloodstain pattern. Each close-up photograph is taken from the same distance as all previous and subsequent close-up photographs. 5) Step 4 is repeated until all scales and selected blood spatter have been photo’d. Close-up Photography of Impact Mechanism Patterns