2 Is it Blood? Obvious Not Obvious Not always an easy determination Stains on clothes, carpet, etc.Presumptive Tests – Blood indicated on…Confirmatory Tests – Blood identified on…Stains not visible (attempted cleaning)Luminol – A type of presumptive test
3 Is it Human Blood? Species determination Different species = different proteinsPrecipitin TestAntibody, antigen testIf human, then the blood will precipitate its protein
4 Blood EvidenceBlood found at a crime scene can be analyzed (utilized as evidence) in a variety of ways:Genetics (molecular make-up for individualization)DNAToxicology (foreign substances i.e. toxins)Drugs, alcoholBloodstain Patterns (how blood was distributed)Spatters
5 Blood Spatters NOT Blood SpLatters – no “L” Crime scene reconstructionValidity of statements made by witness, victim, and suspectInternational Association of Bloodstain Pattern Analysts (IABPA)Organization of forensic experts specializing in the field of bloodstain pattern analysisPromotes education / research and establishes training standards in the field of bloodstain pattern analysis
6 Author:Herbert Leon MacDonellcurrent IABPA HistorianLaboratory of Forensic Science,P.O. Box 1111Corning, NY14830
7 Blood Spatters May Reveal: Origin(s) of bloodstainDistance of bloodstain from targetDirection from which blood impactedSpeed with which blood left its sourcePosition of victim & assailantMovement of victim & assailantNumber of blows, shots, etc.
8 Liquid Blood Physical properties Behaves as a projectile in motion ViscositySurface tensionBoth are about the same as waterBehaves as a projectile in motionGravity as only force – falls verticallyGravity with another force – falls vertically and horizontally at the same time
9 Surface Tension Resistant to penetration & separation Acts to reduce surface areaA sphere offers the smallest surface area to volume ratio so free falling blood drops are spherical (not “teardrop”) on impact
10 Dripping Blood Gravity is the only force acting Blood drop grows until Wt (G) > S.T.Single drop breaks free (teardrop shape)Surface tension pulls in verticallyAnd horizontallyShape settles into sphere (0.05 ml)Does not break up until impact
11 Factors Affecting Drop Size Standard dropsize 50ul (0.05ml)Rapid bleeding givesslightly larger dropShaking/movementcasts off smaller dropsBreaks surface tension...
12 Shape & Size of Bloodspot Depends mostly on nature of target surfaceTexture (rough or smooth)Porous or non porousAngle of impactSize is also related to distance fallenGiven a standard 50 ul drop of bloodThere is little change in spot diameter beyond a fall distance of 4 ft (1.2m)
13 Drop Size vs. Height Fallen Single drops of blood falling from fingertip onto smooth cardboard from various heights.No change in diameter beyond 7 ft.Adapted fromIntroduction to Forensic Sciences,W. Eckert, CRC, 1997
14 Drop Shape vs. Target Surface Spreads out smoothlyST of spreading edge is broken by irregular surface (Micro-droplets)
15 A blood droplet falling from various heights (ft) onto various surfaces (90 degrees) 1.537101.53710Height/Surfacesmoothfloorpapertowelfabric
16 Angle of Impact Elongated shape; more dense at lower edge 90 80 70 605040Elongated shape; moredense at lower edge203010Adapted fromIntroduction to Forensic Sciences,W. Eckert, CRC, 1997
17 Wave Cast-off Angles < 20 degrees to surface David Sadler:Wave Cast-off Angles < 20 degrees to surfaceTail of elongated stainpoints in direction of travel.Tail of wave cast-off pointsback to parent dropParent dropwave cast-off
18 Point of Convergence 5 ml of blood squirted from a syringe from a height of 1mPoint of Convergence
19 Direction and Origin Point of Convergence Point of Origin Two dimensionalShows directionPoint of OriginThree dimensionalShows direction and height
21 Point of Origin Origin Height above point of convergence (Parent Drop) Distance from point of convergenceHeight above point of convergenceOriginlengthwidthAngle of impact = arc sin W/L(Parent Drop)85604530
22 Tracing Origin of Bloodspots Point of convergence method2 dimensional; shows directionPoint of origin method3 dimensional; to include heightIn practice:use of string & protractor at sceneuse of computer at laboratory
23 Blood Spatter Velocity Low velocity (5 f/s, 1.5 m/s)Free-falling drops, cast off from weaponMedium velocity ( f/s, m/s)Baseball bat blowsHigh velocity (>100 f/s, >30 m/s)Gunshot, machinery
24 Low Velocity Blood Spatter Blood source subjected to LV impact< 5 f/s (1.5 m/s)Spot diameter: mostly mmsome smaller, some largerFree-falling drops (gravity only)Cast off from fist, weapon, etc.Dripping (blood droplets into themselves)Splashing (stepping, throwing, etc.)Arterial spurting
25 Cast-off from Weapon First blow causes bleeding Subsequent blows contaminate weapon with bloodBlood is cast-off at a tangent to arc of upswing or backswing (90 degrees)Pattern & intensity depends on:type of weaponamount of blood adhering to weaponlength of arc, swing
32 Cast off Pattern (2/2) Sequence? 1(4 spots)2(3 spots)3(2 spots)If weapon does not pick up more blood, the spatter from subsequent backswings becomes progressively less.In practice weapon picks up more blood with each successful blow.
33 Three overhead swings with a hatchet Direction? Sequence?
47 Arterial Spurt Pattern Blood exiting body under arterial pressure (120 mm Hg); corresponds to heart beatingLarge stains with downward flow on vertical surfaces; air bubbles present if lung was puncturedCreates a wave-like appearance
55 High Velocity Blood Spatter Blood source subjected to HV impact> 100 f/s, 30 m/sFine mist: spot size < 0.1 mmSmall mass limits spread to 1 mSome larger droplets reach furtherGunshotback-spatter from entry woundforward spatter from exit woundHigh speed machinery
56 Gunshot: Back & Forward Spatter Bloodstained foam held just above target surface.Bullet passing L to R just above sheetbullet exits foamBullet entersfoambulletBack spatteron entryForward spatteron exit
57 Gunshot Back Spatter Arises from entrance wound Passes back towards weapon & shooterSeen only at close range of fireSeen on:inside of barrelexterior of weaponhand, arm, chest of shooter
59 Gunshot Forward Spatter Arises from exit woundPasses forward in same direction as shotMore copious than back-spatterCan be seen at any range of fireSeen on nearby surfaces, objects, personsespecially on wall behind victim
60 Forward spatter (5 ms after bullet impacted at 1000 f/s) blood soakedtarget2.5 cm
61 Forward spatter on a target (15cm from exit point) due to a HV impact (bullet) 6” ruler
64 Other Patterns Bloodstain patterns that have been altered Include: Altered by objects, gravity, othersInclude:Wipe PatternsSwipe PatternsTransfer PatternsFlow Patterns
65 Wipe and Swipe Patterns Object moves through a wet bloodstainRemoves and/or alters bloodstain appearanceDoes not require a swipe pattern be presentSwipeTransfer of blood to an unstained surfaceDirection may be determined by feathered edgeA wipe pattern must also be present
66 Transfer Patterns Wet, bloodied object contacts a secondary surface Transfer from:hand, fingersshoes, weaponhairTransfer to:walls, ceilingsclothing, beddingProduces mirror-image of bloodied object
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