Bloodstain Science

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Bloodstain Science. Warning: Some material in this presentation and related videos may be too graphic for some people. Topics. What is Blood? What is blood spatter? Determining Distance of Blood Determining Direction of Blood Types of Blood Stain Patterns Angle of Impact - PowerPoint PPT Presentation

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  • Warning: Some material in this presentation and related videos may be too graphic for some people.

  • TopicsWhat is Blood?What is blood spatter?Determining Distance of BloodDetermining Direction of BloodTypes of Blood Stain PatternsAngle of ImpactHow is blood stain detected at crime scenes

  • What is Blood?

  • Introduction to Blood

  • Blood Spatter (or splatter)Blood drops form different shapes and sizesBlood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

  • Determining Distance Blood FallsBlood drops fall as small spheresBlood Spatter > Distance

  • Determining Distance Blood FallsDrops form circle when hitting surfaceSize depends on speed of blood dropBlood Spatter > Distance

  • Determining Distance Blood FallsFaster drop = larger diameter (size)Higher distance = larger diameterDue to air resistance, speed maxes out at distances above about 7 feetBlood Spatter > Distance

  • Determining Distance Blood FallsHowever, size of drop also depends on the volume of the drop.Volume depends on the object blood originated from (needle = small; bat = large).Blood Spatter > Distance

  • Determining Distance Blood FallsSince the volume of blood is unknownThe distance a drop has fallen cannot be measured.Blood Spatter > Distance

  • Effect of SurfaceSmooth surface = smooth sphereRough surface may cause some splatterBlood Spatter

  • Determining Direction of BloodNarrow end of a blood drop will point in the direction of travel.Blood Spatter > Direction

  • Determining Direction of BloodIf more than one drop (from spatter) results, the point of origin can be determinedBlood Spatter > Direction

  • Determining Direction of BloodIf more than one drop (from spatter) results, the point of origin can be determinedBlood Spatter > Direction

  • Determining Direction of BloodThis is a 2-dimensional point of origin. It is possible to determine the 3-D point of originBlood Spatter > Direction

  • Determining Direction of BloodThe angle can be determined mathematically. Width/Length, then take the inverse sin (sin-1).This number is the impact angle (90 = perpendicular to surface; Direction

  • For each blood drop, a string can be guided back to the point of origin. Blood Spatter > Direction

  • Types of SpatterSpattered Blood = random distribution of bloodstains that vary in sizeAmount of blood and amount of force affect the size of blood spatter.Can result from gunshot, stabbing, beatingBlood Spatter

  • Spattered Blood can:Help determine the location of the origin of the blood source.Help determine the mechanism which created the pattern.Blood Spatter

  • Spattered BloodIn general, for higher impacts, the pattern is more spread out and the individual stains are smaller.Low impact = beating High impact = gunshotBlood Spatter

  • Types of SpatterGunshot Spatter = can result in a mist-like spatter that indicates a gunshot. Not all gunshots will result in misting.If misting is present, it is most likely a gunshot.Blood Spatter

  • Gunshot SpatterGunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits). Blood Spatter

  • Types of SpatterBeating and Stabbing Spatter = larger individual stainsFirst blow usually doesnt result in spatter since there is not yet any exposed blood.Blood Spatter

  • Types of SpatterSatellite Spatter = free falling drops of blood that fall onto a spatter pattern. These drips are usually much larger than impact spatter.However, blood dripping into blood can create a spatter.Blood Spatter

  • Types of SpatterCastoff Pattern = Blood flung off of swinging object. Can reconstruct where assailant and victim were positioned. Blood Spatter

  • Types of SpatterExpirated Bloodstain Pattern = Blood can accumulate in lungs, sinuses, and airway. Forcibly exhaled. Can appear like beating or gunshot pattern.May be mixed with saliva or nasal secretions.Blood Spatter

  • Alteration of bloodstain over timeBlood dries and clots over time.Difficult to estimate the time the blood exited the body.Clotted smears can indicate time of movement.Blood Spatter

  • What does the abbreviation BPA represent? Bloodstain Pattern Analysis

    What can an investigator learn from the analysis of a blood spatter? Type and velocity of weapon Number of blows Handedness of assailant (right or left-handed) Position and movements of the victim and assailant during and after the attack Which wounds were inflicted first Type of injuries How long ago the crime was committed Whether death was immediate or delayedHow does a blood droplet form? Click the image for an animation.Source: http://science.howstuffworks.com/bloodstain-pattern-analysis1.htm

  • Blood which impacts a surface at a 90 degree angle will be nearly round in shape.As the blood impacts at a angles decreasing from 90 degrees the pattern will become more elongated and elliptical.The angle of impact is that between the surface and angle line.

    Angle of Impact

  • - Direction of travel refers to the direction in which the blood spatter is moving from its origin to its destination. - It can be determined from spatters from the tail . -In free flow and swipes and wipes it can be determined by spatial relationships and feathering of the pattern.A line drawn through the center of the longest aspect (axis) of the stain, and in the direction of the tail points in the direction of travel.Direction of Travel of Bloodstain Patterns

  • Light SourceInvestigators will first examine the crime scene to look for areas that may contain blood. They may use a high-intensity light or UV lights to help them find traces of blood as well as other bodily fluids that are not visible under normal lighting conditions. How is blood evidence detected at a crime scene?Blood Reagent TestsThese tests, referred to as presumptive tests, are used to detect blood at crime scenes based upon the properties of hemoglobin in the blood. Further tests at the crime lab can determine if it is human blood or not.

    Examples:

    Phenolphthalein is a chemical that is still utilized today and is usually referred to as the Kastle-Meyer test and produces a pink color when it reacts with hemoglobin.

    HemaStix is a strip that has been coated with tetramethylbenzidine (TMB) and will produce a green or blue-green color with the presence of hemoglobin.Kastle-Meyer TestVideoHemaStix

  • Luminol This chemical is used by crime scene investigators to locate traces of blood, even if it has been cleaned or removed. Investigators spray a luminol solution is throughout the area under investigation and look for reactions with the iron present in blood, which causes a blue luminescence. One problem is that other substances also react, such as some metals, paints, cleaning products, and plant materials. Another problem is that the chemical reaction can destroy other evidence in the crime scene. LCV or Leuco Crystal Violet, is one type of chemical process that is used for blood enhancement. Using this test helps to make the blood evidence more visible so it can be photographed and analyzed.FluoresceinThis chemical is also capable of detecting latent or old blood, similar to luminol. It is ideal for fine stains or smears found throughout a crime scene. After the solution has been sprayed onto the substance or area suspected to contain blood, a UV light and goggles are used to detect any illuminated areas, which appear greenish-white if blood is present. It may also react to many of the same things as luminol (copper and bleach). Fluorescein Reaction in UV Light

  • Bloodstain Pattern Analysis TermsSpatter Bloodstains created from the application of force to the area where the blood originated.Origin/Source The place from where the blood spatter came from or originated.Angle of Impact The angle at which a blood droplet strikes a surface.Parent Drop The droplet from which a satellite spatter originates.Satellite Spatters Small drops of blood that break of from the parent spatter when the blood droplet hits a surface.Spines The pointed edges of a stain that radiate out from the spatter; can help determine the direction from which the blood traveled.

  • Passive BloodstainsPatterns created from the force of gravityDrop, series of drops, flow patterns, blood pools, etc.Types of Bloodstain Patterns

  • Use your results to answer these questions.

    What did you notice about the diameter of the parent droplets as you increased the height of the drop?

    How do the spines compare from the different heights?

    Blood Spatter Lab 1 Questions

  • Use your results to answer these questions.

    What happened when one drop landed on top of another one?

    What did you notice about the diameter of the parent droplets as you increased the height of the drop?

    What do you notice about the diameter of the satellite spatter as you increased the height of the drop?

    Lab 1 Questions

  • Use your results to answer the question.

    What did you notice about the shape of the droplets as you increased the angle of the paper?

    Lab 2 Questions

  • If you find a trail of blood with droplets that are round and close together, what could this mean?

    **

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