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Forensics Expert Explains How to Analyze Bloodstain Patterns | WIRED - YouTube
Channel: WIRED
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foreign
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there we go hi I'm Matthew Steiner Matt
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is a certified senior crime scene
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analyst he's explained crime scene
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forensics in technique critique
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so that's a really interesting yet very
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illegal way to get DNA from somebody
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today I'm going to show you how to
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analyze various blood stain patterns
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so we'll learn the techniques forensics
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experts used to investigate blood stain
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patterns ranging from easy to difficult
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so normally when we go to a crime scene
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it's not set up like this unless we have
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some sort of Dexter X crime scene where
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the Killer really planned it out today
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we're doing on set for safety purposes
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for us at crime scenes when we
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investigate them safety is number one we
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want to protect ourselves I think we
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various bloodborne pathogens that we're
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dealing with and secondly we don't want
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to contaminate the crime scene so we
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don't want the hairs and fibers on
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ourselves the DNA that's shedding off Us
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Falling onto our evidence at a crime
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scene we'd wear multiple layers of
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gloves if we're going to be handling
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evidence and then we'd want to wear eye
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protection if there's like a splash
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Hazard with blood that hasn't been dried
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so our Tyvek suit covers most of our
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body including our feet because we want
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to be introducing our shoe wear
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Impressions into a crime scene or
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destroying evidence that's there so
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normally I'd be wearing a mask but I
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don't think it's a really good look for
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talking on camera next we're going to
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talk about the three main categories of
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blood stains that we can encounter at a
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crime scene
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foreign
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we're going to be using defibrinated
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sheep's blood we have taken the fibrin
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out of this blood fibrin is a protein
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that's in our plasma that causes our
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blood to clot so if we use regular whole
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blood that had fibrin in it we'd have a
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clotted mess inside this bottle let's
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say pattern analysts correlate the
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appearance of these blood stain patterns
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at a crime scene to a mechanism by which
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they were created it isn't a crystal
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ball it isn't like the way TV presents
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it where a prime scene investigator
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walks into a scene and could tell you
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every single action that happened inside
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that crime scene from beginning to end
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analysts can correlate the static blood
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stains at a crime scene with Dynamic
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forces that create them so we look at is
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specific stain patterns and we could
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figure out how they possibly were
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created and then with that we could show
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a small window of time not the whole
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crime but that this type of force could
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have created this sort of pattern so
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passive patterns are patterns that are
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created without any sort of outside
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external Force other than gravity or
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contact so we're going to first start
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off with avoid dropping blood at 90
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degrees to see what we get so I'm going
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to take
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pipette
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and a small amount of blood and hold it
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directly above and drop it so when our
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sphere of blood strikes the surface at
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90 degrees we have a very even round
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circle at a crime scene but also what
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affects the way our blood stain looks is
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the surface itself we have Plexiglas and
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we notice that the edge characteristics
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of our bloodstain are very even now that
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we observed the way that blood acts on a
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smooth surface let's try tile which has
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a little bit of texture to it one drop
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of blood
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straight down onto a different surface
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now
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you can see a little bit of scalloping
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around the edges there that's because of
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the surface texture so the scalping is
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just the different ways that we describe
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the edge characteristics of blood stains
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so it could be smooth uniform it could
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be scalloped or it could be spiny
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so now we change the surface to a
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rougher surface wood so we can see a
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vast difference from where we started
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where we have smooth edge
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characteristics
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now we have the spinier pattern because
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that blood drop is being disrupted by
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the surface itself and we can also see
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we have some satellite stains satellite
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stains are stains that come off of
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parent stain so this main stain here is
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my parent stain in this case because the
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disruption they are being forced out
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from the center of it we also see
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satellite spatter when blood is being
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dripped into blood typically at a crime
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scene especially with stabbings we want
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to look for these drip patterns it could
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be that the suspect accidentally cuts
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themselves and they're moving around a
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crime scene and fleeing the crime scene
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and they could leave blood trails that
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we could follow next we're going to be
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looking at contact transfer stands a
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transfer pattern is a passive pattern
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where we have a bloody surface coming in
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contact with another surface and then
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sometimes we could actually figure out
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what made that transfer whether it was a
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hand or a weapon or someone's clothing I
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mean that's the best type of evidence
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that we could have at a crime scene is
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we have the victim's blood and we have
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the suspect's impression there's very
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few explanations of how that happens so
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we're going to start off with a shoe our
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impression and blood so this could be
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our victim Walking Through Blood
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creating patterns in our crime scene or
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this could be the suspect's shoe wear
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impression we're going to coat the
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bottom of the shoe and we're going to
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transfer the pattern at the bottom of
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the shoe to our clean surface so I have
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my shoe wear that's completely coated in
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Blood and then inside that crime scene
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we have a transfer of that pattern
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and we'll notice is that that pattern
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gets lighter and lighter as we move
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along what we don't see with our naked
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eye we could find later on with
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chemicals like luminol or blue star so
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we could see a continuation of that
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pattern as someone walks away from a
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crime scene sometimes we see transfer
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patterns in textiles so next we're going
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to take some blood saturate a portion of
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our genes with it and we're going to
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transfer that onto our surface so
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sometimes in real crime scenes these get
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misinterpreted as the lines of minutia
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in your fingerprints or palm print we
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would see is that unlike fingerprints or
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just straight lines either way we would
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document this and collect it and send to
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the lab and then under magnification
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analyze it so next we're going to
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discuss how movement could affect these
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transfer stain patterns so I'm going to
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take some blood and put it onto my hand
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and then move that across the surface so
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if I touch the surface and then move my
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hand we see what's called Feathering the
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effect of movement on blood just like if
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I took a paintbrush and moved it across
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the wall in the beginning it would be
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darker but eventually it would get
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lighter so if this Feathering effect
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helps us interpret movement at a crime
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scene this could be found at a crime
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scene in many different ways one could
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be our suspect has blood on their hands
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and they move it across a clean surface
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and another very common way that we see
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these patterns at a crime scene are
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what's called drag marks we have a
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victim that's bleeding and either
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they're moving through the scene or
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someone's dragging them through the
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scene and we'd see the same effect that
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Feathering going towards the body next
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we're going to cover a flow patterns and
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that is the volume of blood being
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affected by gravity so we can see here
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is that gravity is pulling upon that
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blood and pulling it down on our surface
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at crime scenes this may be very
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valuable evidence when we observe our
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victims injuries person had an injury to
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their shoulder if they're standing or if
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their body is erect that flow pattern
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should go straight down in our arm but
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if they've been moved or this movement
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or that injury was caused when they're
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laying down we'd see a different flow
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pattern so next we're going to discuss
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saturation and pooling pattern that we
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have at a crime scene saturation pulling
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patterns could tell us that someone is
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bleeding in a certain part in a crime
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scene for a period of time you know
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sometimes when we see Bubbles at a scene
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that could mean that we have a expirated
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pattern or a pattern that's coming from
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an airway but let's pop those because we
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don't want but what this could tell me
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is that we had accumulation of blood
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there and that there has been no
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movement because if this happened and
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then we moved the shirt we would see
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that the blood would move in that
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direction typically we'll see this on
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mattresses or beds or bedding and then
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it would absorb a little more so now
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we're going to have an accumulation of
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blood on a non-porous surface and we'll
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see pooling so pooling and saturation
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it's the same mechanism we're looking at
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just the accumulation of blood but
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pulling the blood is not being absorbed
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into the surface for pools of blood what
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we'll see with actual whole blood that
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has fibrin in it they will dry a lot
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slower than it would in something that
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absorbent but also we're going to see
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over a period of time is clotting inside
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that pool and then sometimes we'll see
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affect what's called serum separation so
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the edges of this will be clear where we
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see the plasma of the blood as it
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separates so now we're moving on to the
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spatter category of bloodstain pattern
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analysis with this category of blood
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stains we're looking at some sort of
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external force on an open source of
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blood so I'm going to do is I'm going to
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put a small amount of blood on our wood
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here I'm going to strike it with a
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hammer and what we should see is that
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impacts batter on the Plexiglas in front
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of us put on my goggles I'm going to put
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my hood up
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give us a small amount of blood here all
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right ready
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there we go
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so as you can see
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not only do we have impact spatter on
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the plexiglass in front of us we also
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have it on our suspect here okay so we
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applied Forest to an open source of
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blood and we have a resulting impact
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stain our stain pattern what we'll
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notice is directly opposite where the
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force was applied we have our blood
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striking that surface at 90 degrees so
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these stains that we have right here
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near the bottom are circular but the
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further we move away from that Source
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these blood stains are now hitting this
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surface at an angle so our stains are
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more elliptical bludgeoning would be the
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most common way that we get these stains
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but it could be that we have the force
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of a bullet passing through somebody so
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we have a phenomenon called forward
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spatter and back spatter so if someone
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is shot and if bullet passes through say
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their shoulder
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we have blood going in the direction of
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the force or with the bullet out of the
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exit but we also have blood going the
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opposition of the force and that's what
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we call back spatter first up we started
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by creating different patterns so we
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could analyze Next Step we're going to
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look at something a little more
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difficult
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[Music]
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next we do is calculate the area of
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convergence that's a two-dimensional
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area on our surface if we draw a line
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through the long axis of several stains
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where all these lines will meet they
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should converge in an area somewhere in
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the center here what I want to do is
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pick several stains
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that are elliptical
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from different sides of the pattern
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we're looking at this to solve where
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this blood came from I'm going to start
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with this stain here
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and I'm going to line up so that I'm
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drawing
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a line through the long axis of my stain
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so this is where the tail is going to
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help me out to figure out the
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directionality but also to line up my
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ruler
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and then sometimes what we'll do is just
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kind of show for a jury an arrow the
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direction that stainless going so then
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I'll move around the pattern from
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different sides of it and draw through
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different stains so this isn't done in
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every crime scene but when we have a
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pattern like this we have elliptical
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stains along the outside and we have
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some circular stance towards the inside
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this is the perfect opportunity for us
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to do some analysis I could keep going
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and draw more lines through more stains
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and it should all be coming back to the
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same general direction so if this was on
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the wall and this is very low you know
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this could be very powerful evidence to
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show that you know that that was low to
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the ground where this impact happened
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since we identify different stains that
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are striking our surface at different
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angles we're going to figure out the
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angle of impact that these stands hit
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our surface we do that by measuring the
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length of the stain we divide it into
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the width of the stain and the arc side
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of that number will give us our angle of
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impact so we're measuring stains we
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always want to use millimeters allows us
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for smaller measurements so what we
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could also use is a digital caliper and
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that will give us precise sub millimeter
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measurements
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so I want to measure the length of the
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stain the long axis of the stain so this
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is 3.1 millimeters and then I'd measure
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the width of it so I'm measuring the
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widest part of the stand that's 1.7
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millimeters we're going to divide 3.1
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into 1.7 so if we do the arc sine of
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that number that will give us the angle
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of impact which is 33.25
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if you had a regular ruler you would
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just have to round up to the closest
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millimeter so in this case this stain is
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four millimeters
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and then we measure the width of it it
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is two millimeters
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so we would divide
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four into two which gives us 0.5
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and the arc sine of 0.5 is 30 degrees
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and we can see this basically at the
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same distance from our Center but just
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on the other side if we look at this two
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dimensionally we know that these lines
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of our area of convergence meet here but
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if I want to think about it
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three-dimensionally that my blood is
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coming from somewhere above it here so
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the next step will be is that we're
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going to calculate the area of origin if
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it's coming in at a right angle here I
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have a triangle so this would be my
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adjacent side of the triangle I know
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that it's 90 degrees from here
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so that's my right triangle
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and then this side that the path takes
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is the hypotenuse of the triangle
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and so if I know the distance from my
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stain
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to my area of convergence
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and I want to figure out how far away my
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area of origin is here in space
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if I do the tangent of that I could
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figure out the side like sohcahtoa
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when we analyze blood sense in a field I
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always feel it's better to do all these
[807]
methods we should be coming up with
[809]
similar results but if you messed up
[810]
somewhere you know one of those is going
[812]
to be correct next up we're going to try
[814]
something a little more difficult
[815]
interpreting relationships
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foreign
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there's an adage that forensic science
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is the art of observation governed by
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science
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so we have observed our stain patterns
[829]
at our crime scene and we're going to
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interpret how these possibly were
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created so if I go to a crime scene and
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I see that there's some clothing there
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eventually I'm going to recover this but
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after I recover it and I see that
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there's passive stance underneath it I
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know that this came after this that this
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wasn't in place that this was placed
[847]
afterwards and if I don't see a transfer
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of blood on here it could be that this
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was a ready dry by the time this
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clothing went on top of it so now we're
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looking at a passive drug pattern
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this could be the victim's blood this
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could be the suspect's blood we won't
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know until we sample it and send it off
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for analysis what we can interpret from
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this could be movement so if this trail
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of blood is leading away from the scene
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we would see those Tails going in a
[873]
direction of travel
[874]
now we're looking at a white pattern we
[876]
have a pre-existing stain
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that something came in contact and moved
[880]
through it so we could see from our
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discussion earlier Feathering that the
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directionality is coming towards me
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something is passively dripping blood
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that could be a weapon that could be a
[892]
victim that could be our suspect and
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then something later on comes through it
[895]
that could be someone trying to clean up
[897]
the stain this could also be that maybe
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someone was dragged through this or
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there was some sort of movement through
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that stain
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so that was a white pattern now we have
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a swipe pattern blood is on something
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here and we could see again that same
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Feathering going in the direction of
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travel we have a transfer pattern with
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movement which is a swipe pattern
[918]
there's blood on something and then
[920]
we're just moving that in a direction
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usually when it's a white pattern we
[923]
could see those original stains so the
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drawing and then someone tries to wipe
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them off with a cloth now we're looking
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at a cast off pattern so this is a
[932]
subcategory spatter that's a projection
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mechanism so blood is on an object and
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removing that object in space that could
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be someone's hand that could be a pipe
[941]
that could be a bat that could be a
[943]
knife and as that object moves blood
[946]
will be flung off it and we have these
[948]
very distinct linear patterns or curvy
[950]
linear patterns at a crime scene if we
[953]
see these cast off patterns they can go
[955]
up the walls they can go across the
[957]
floor and even onto the ceiling so we're
[959]
looking at a spatter pattern but we have
[961]
a normally continuous drops of blood
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that are being interrupted or blocked by
[966]
something and that gives us a pattern
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What's called the void sometimes we have
[969]
crime scenes where there's something
[970]
important that would be in that
[973]
pool or in that pattern or that spatter
[975]
pattern and it's been removed so it
[977]
could be someone's bag or a cell phone
[980]
their wallet if I had a crime scene
[982]
where someone was bludgeoned and
[985]
adjacent to his head was the complete
[989]
absence of
[990]
uh blood spatter looking to the left of
[993]
him there was a spatter pattern it
[995]
didn't line up what we determined was
[997]
that the curtains inside of the hotel
[999]
room were open at the time of the crime
[1001]
and then closed later on we've gone over
[1004]
how these patterns are created or
[1006]
different categories of patterns and
[1008]
what we can interpret from these
[1009]
patterns at a crime scene this is not a
[1012]
simple process this stuff takes time
[1013]
training and experience and beyond that
[1016]
there's no absolutes with any of this
[1018]
there's no one specific answer then it's
[1020]
only that one answer I hope you guys
[1022]
learned a lot
[1023]
[Applause]
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