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A Bloody Mess

A BLOODY MESS HOW BLOODSTAIN PATTERN ANALYSIS WORKS When a crime scene ihvolves blood, you know it's bad. Someone may be hurt or dead, and figuring out who and why becomes urgent. That's why law enforcement officials call upon experts in bloodstain pattern analysis, or BPA, to determine what happened as quickly as possible. Every drop of blood tells a story- what may surprise you is these stories' amazing depth of detail. WHAT BPA CAN DETERMINE fig. 1 fig. 2 fig. Movements/position of those involved Date and time of cri me Type and velocity of weapon fig. 4 fig. 5 fig. 6 a. b. O- If the assailant was "teft or right handed Types of injuries dealt Whether death was i mmediate BLOOD AND YOUR BODY In the human body, blood accounts for roughly 8% of body weight. MALE: 5-6 L 2 liter soda bợttle FEMALE: 4-5 L If 1.5L of blood are lost, unconsciousness may occur. Death becomes a risk at 40% blood loss. THE TYPES OF SPATTER IMPACT SPATTERS LOW-VELOCITY FORCE OF IMPACT: 5 feet per second (fps) or 1ess DROPLET DIAMETER: 4-8mm POSSIBLE SOURCE: dripping blood, "passive spatters" MEDIUM-VELOCITY FORCE OF IMPACT: 5-100 fps DROPLET DIAMETER: less than 4mm POSSIBLE SOURCE: blunt object, fist, stabbing, artery spray HIGH-VELOCITY FORCE OF IMPACT: >100fps DIAMETER: 1less than 1mm POSSIBLE SOURCE: gunshot wounds OTHER BLOODSTAIN PATTERNS fig. 1 fig. 2 fig. 3 SHADOWING/ GHOSTING CAST-OFF STAINS SWIPES AND WIPES When there is an empty space, or "void" in spatter, indicating that an object blocked Swipes occur when blood on a surface is When blood on an object that is swung through space flies off onto a surface. smeared, and wipes occur when a bloody object brushes against a surface. spray. fig. 4 fig. 5 EXPIRATORY BLOOD TRANSFER PATTERN The bloodstain pattern Blood that is coughed up or breathed out. Misty pattern resem- bling high-velocity spatter results. left on a surface after a bloody object has been placed on it. ANALYZING THE PATH OF A BLOOD DROPLET After determining the type of spatter and weapon likely used, forensic analysts look at the shape of individual droplets to mathematically determine their point of origin. fig. 1 Though blood droplets form at the edge of a surface as teardrops, they travel as spheres. fig. 2 The diameter of a blood stain increases with the height from which it was dropped. fig. 1 6 in 1 ft 2 ft 3 ft fig. 2 4 ft 5 ft 6 ft 7 ft CALCULATING THE IMPACT ANGLE The shape of a droplet also changes with the angle at which it strikes the surface. The sharper the angle, the longer the tail. Analysts can use the dimensions of the droplet to determine the angle at which it hit the surface by dividing its width by its length, then taking the arcsin of that number: ANGLE OF IMPACT = ARCSIN WIDTH LENGTH fig. 1 fig. 2 fig. Enlongation of droplet occurs upon impact MOVING BLOOD DROPLET IMPACT (SIDE VIEW) IMPACT (TOP VIEW) 90° 80° 70° CSI 60° 40° 20° 10° Investigators then employ 'stringing' of all blood droplets through the air origin (the strings' point of convergence). using strings to chart the trajectories to determine the blood's point of TYPES OF WOUNDS If no victim is present, forensic analysts can use the information gathered from BPA to assess what kinds of wounds may have been dealt: fig. 1 fig. 2 fig. 3 INCISIONS LACERATIONS PENETRATION WOUNDS Thin wound caused bya sharp-edged object such as a knife. Tear wounds caused by blunt trauma. Occur when a sharp object is inserted and pulled out of the skin. Spatter: Low- velocity, wipe Spatter: Low- or medium - velocity Spatter: Low - and medium - velocity fig. 4 fig. 5 fig. 6 GUNSHOT WOUNDS ABRASIONS PUNCTURE WOUNDS Caused by a thin, pointy object punctur- ing the skin. Caused by a bullet or other high-velocity projectile entering the skin. May result in two wounds (entry and exit). Scrapes caused by sliding against a rough surface. Spatter: Low-velocity, wi pe Spatter: Wipes Spatter: High- velocity CREATED BY FORENSICNURSING.ORG REFERENCES: http://www.sho.com/site/dexter/blood_spatter.do http://science.howstuffworks.com/bloodstain -pattern-analysis, htm . http://www.bloodspatter.com/BPATutorial.htm http://projects.nfstc.org/gallery/main.php?g2_itemId-3857, http://en.wikipedia.org BY NC ND This work is licensed under a Creative Commons License, ......----

A Bloody Mess

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This infographic provides a step by step visual that shows how blood stain pattern analysis works to determine the cause and method of death.

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