Forensics Expert Explains How to Analyze Bloodstain Patterns | WIRED

there we go hi I'm Matthew Steiner matt is a certified senior crime scene analyst he's explained crime scene forensics in technique critique so that's a really interesting yet very a legal way to get DNA from somebody today I'm going to show you how to analyze various blood stain patterns in this episode we'll learn the techniques forensics experts use to investigate blood stain patterns ranging from easy to difficult so normally when we go to a crime scene it's not set up like this unless we have some sort of Dexter X crime scene where the killer really planned it out today we're doing on set for safety purposes for us at crime scenes when we investigate them safety is number one we want to protect ourselves I think we various blood-borne pathogens that we're dealing with and the secondly we don't want to contaminate the crime scene so we don't want the hairs the fibers on ourselves the DNA the shedding off us falling onto our evidence at a crime scene we'd wear multiple layers of gloves if we're gonna be handling evidence and then we'd want to wear eye protection if there's like a splash hazard with blood that hasn't been dried so our Tyvek suit covers most of our body including our feet because we want to be introducing our shoe wear impressions into a crime scene or destroying evidence that's there so normally I'd be wearing a mask but I don't think it's really good look for talking on camera next we're going to talk about the three main categories of bloodstains that we can encounter at a crime scene today we're going to be using defibrillated sheep's blood we have taken the fibrin out of this blood fibrin is a protein that's in our plasma that causes our blood to clot so if we use regular whole blood that had the fibrin in it we'd have a clotted mess inside this bottle let's same pattern analysts correlate the appearance of these blood stain patterns at a crime scene to a mechanism by which they were created it isn't a crystal ball it isn't like the way TV presents it where a crime scene investigator walks into a scene and could tell you every single action that happened inside that crime scene from beginning to end analysts can correlate the static bloodstains at a crime scene with dynamic forces that create them so we look at is specific stain patterns and we could figure out how they possibly were created and then with that we could show a small window of time not the whole crime but that this type of force could have created this sort of pattern so passive patterns are patterns that are created with database and outside external force other than gravity or contact so we're gonna first start off with dropping blood at 90 degrees to see what we get so I'm going to take pipette and a small amount of blood and hold it directly above and drop it so when our spear of blood strikes a surface at 90 degrees we have a very even round circle at a crime scene but also it affects the way our blood stain looks is the surface itself we have Plexiglas and we noticed that the edge characteristics of our blood stain are very even now that we observed the way that blood acts on a smooth surface let's try tile which has a little bit of texture to it one drop of blood straight down onto a different surface now you could see a little bit of scalloping around the edges there that's because of the surface texture so the scalloping is just of different ways that we describe the edge characteristics of bloodstains so it could be smooth uniform it could be scalloped or it could be spiny so now we change our surface to a rougher surface wood so we see a vast difference from where we started we have smooth edge characteristics now we have the spiny err pattern because that blood drop is being disrupted by the surface itself and we can also see we have some satellite stains satellite stains are stains that come off of aren't stained so this main stain here is my parents stain in this case because the disruption they are being forced out from the center of it we also see satellite spatter when blood is being dripped into blood typically at a crime scene especially with stabbings we want to look for these drip patterns it could be that the suspect accidentally cuts themselves and they're moving around a crime scene and fleeing the crime scene and they could leave blood trails that we could follow next we're gonna be looking at contact transfer stands a transfer pattern is a passive pattern where we have a bloody surface coming in contact with another surface and then sometimes we could actually figure out what made that transfer whether it was a hand or a weapon or someone's clothing I mean that's the best type of evidence that we could have at a crime scene so we have the victim's blood and we have the suspects impression there's very few explanations of how that happens so we're gonna start off with a shoe wear impression in blood so this could be our victim walking through blood creating patterns in our crime scene or this could be the suspects shoe wear impression we're gonna coat the bottom of the shoe and we're gonna transfer the pattern at the bottom of the shoe to our clean surface now I have my shoe wear that's completely coated in blood and then inside that crime scene we have a transfer of that pattern and we'll notice is that that pattern gets lighter and lighter as we move a lot what we don't see what our naked eye we could find later on with chemicals like luminol a blue star so we could see a continuation of that pattern as someone walks away from a crime scene sometimes we see transfer patterns in textiles so next we're gonna take some blood saturate a portion of our jeans with it and we're gonna transfer that onto our surface so sometimes in real crime scenes these get misinterpreted as the lines of minutiae and your finger prints or palm print we would see is that unlike fingerprints are just straight lines either way we would document this and collect it and sensor lab and then under magnification analyze it so next we're gonna discuss how movement could affect these transfers stain patterns so I'm gonna take some blood and put it onto my hand and then move that across the surface so if I test a surface and then move my hand we see what's called feathering the effective movement on blood just like if I took a paint brush and moved it across a wall and in the beginning would be darker but eventually it would get lighter so this feathering effect helps interpret movement at a crime scene this could be found at a crime scene in many different ways one could be our suspect has blood on their hands and they move it across a clean surface and another very common way that we see these patterns at a crime scene or what's called drag marks we have a victim that's bleeding and either they're moving through the scene or someone's dragging them to the scene and we'd see the same effect that feathering going towards the body next we're gonna cover a flow patterns and that is a volume of blood being affected by gravity so we can see here is that gravity is pulling upon that blood and pulling it down on our surface at crime scenes this may be very valuable evidence when we observe our victim's injuries person had an injury to their shoulder if they're standing or if their body is erect that flow pattern should go straight down their arm but if they've been moved or this movement or that injury was caused when they're laying down we'd see a different flow pattern so next we're gonna discuss saturation and pooling patterns that we have at a crime scene saturation and pooling patterns could tell us that someone is bleeding and a certain part in a crime scene for a period of time you know sometimes when we see bubbles at a scene that could mean that we have a expert a pattern or a pattern that's coming from airway but let's pop those because we don't but what this could tell me is that we had accumulation of blood there and that there's been no movement because if this happened and then we moved the shirt we would see that the blood would move in that direction typically we'll see this on mattresses or beds or bedding and it would absorb a little more so now we're going to have an accumulation of blood on a non-porous surface and we'll see pooling so pooling and saturation it's the same mechanism or looking at just the accumulation of blood but what pooling the blood is not being absorbed into the surface for pools of blood what we'll see with actual whole blood that has fibrin in it they will dry a lot slower than it would in something that's absorbent but also we're going to see over a period of time is clotting inside that pool and then sometimes we'll see effect what's called serum separation so the edges of this will be clear where we see the plasma of the blood as it separates so now we're moving on to the spatter category of blood same pattern Alice with this category of bloodstains we're looking at some sort of external force on an open source of blood so I'm gonna do is gonna put a small amount of blood on there wood here I'm gonna strike it with the hammer and what we we should see is an impact spatter on the Plexiglas in front of us put on my goggles I'm gonna put my hood up a small amount of blood here all right you ready there we go so as you can see not only do we have impact spatter on the Plexiglas in front of us we also have it on our suspect there okay so we applied force to an open source of blood and we have a resulting impact stain our stain pattern what we will notice is directly opposite where the force was applied we have our blood striking that surface at 90 degrees so these things that we have right here near the bottom are circular but the further we move away from that source these bloodstains are now hitting this surface at an angle so our stains are more elliptical bludgeoning would be the most common way that we get these stains but it could be that we have the force of a bullet passing through somebody so we have a phenomenon called forward spatter and back spatter so if someone is shot and the bullet passes through say their shoulder we have blood going in the direction of the force or with the bullet out of the exit but we also have blood going the opposition of the force and that's what we call back spatter first up we started by creating different patterns so we could analyze next step we're gonna look at something a little more difficult [Music] next we do is calculate the area of convergence that's a two-dimensional area on our surface if we draw a line through the long axis of several stains where all these lines will meet they should converge in an area somewhere in a center here what I want to do is pick several stains that are elliptical from different sides of the pattern we're looking at this to solve where this blood came from I'm gonna start with this stain here and I'm going to line up so that I'm drawing a line through the long axis of my stain so this is where the tail is gonna help me out to figure out the directionality but also to line up my ruler and then sometimes what we'll do is just kind of show for a jury an arrow the direction that stain is going so then I'll move around the pattern from different sides of it and draw through different stains so this isn't done at every crime scene but when we have a pattern like this we have elliptical stains along the outside we have some circular stance towards the inside this is the perfect opportunity for us to do some analysis I could keep going and draw more lines through more stains and it should all be coming back to the same general direction so if this was on the wall and this is very low you know this could be very powerful evidence to show that you know that that was low to the ground where this impact happened since we identified different stains that are striking our surface at different angles we're gonna figure out the angle of impact that these stains hit our surface we do that by measuring the length of the stain we divide it into the width of the stain and the arcsine of that number will give us our angle of impact so we're measuring stains we always want to use millimeters allows us for smaller measurements so what we could also use is a digital caliper and that will give us precise submillimetre measurements so I want to measure the length of the stain long axis of the stain so this is 3.1 millimeters and then I'd measure the width of it so I'm measuring the widest part of the same that's one point seven millimeters we're gonna divide three point one into 1.7 so if we do the arcsine of that number that will give us the angle of impact which thirty three point two five if you had a regular ruler you would just have to round up to the closest millimeter so in this case this stain is four millimeters and then we measure the width of it two millimeters so we would divide 4 into 2 which gives us point five and the arcsine of 0.5 is thirty degrees and if we can see this basically at the same distance from our Center but just on the other side if we look at this two dimensionally we know that these lines of our area of Bridgett's meet here but if I want to think about it three dimensionally that my blood is coming from somewhere above it here so the next step will be is that we're gonna calculate the area of origin if it's coming in at a right angle here I have a triangle so this would be my adjacent side of the triangle I know that it's 90 degrees from here so that's my right triangle and then this side that the path takes is the hypotenuse of the triangle and so if I know the distance from my stain to my area of convergence and I want to figure out how far away my area of origin is here in space if I do the tangent of that I could figure out the side like sohcahtoa when we analyze bloodstains in a field I always feels better to do all these methods we should coming up with similar results but if you messed up somewhere you know one of those is going to be correct next up we're gonna try something a little more difficult interpreting relationships there's an adage that forensic science is the art of observation governed by science so we have observed our stain patterns at our crime scene and we're going to interpret how these possibly were created so if I go to a crime scene and I see that there's some clothing there eventually I'm going to recover this but after I recover it and I see that there's passive stains underneath it I know that this came after this that this wasn't in place that this was placed afterwards and if I don't see a transfer a blood on here it could be that this was already dry by the time this clothing went on top of it so now we're looking at a passive drug pattern this could be the victim's blood this could be the suspects blood we won't know until we sample it and send it off for analysis what we can interpret from this could be movement so if this trail of blood is leading away from the scene we would see those tails going in a direction of travel now we're looking at a white pattern we have a pre-existing stain that something came in contact and move through it so we could see from our discussion earlier feathering that the directionality is coming towards me something is passively dripping blood that could be a weapon that could be a victim that could be our suspect and then something later on comes through it that could be someone trying to clean up the stain this could also be that maybe someone was dragged through this or there was some sort of movement through that stain so that was a white pattern now we have a swipe pattern blood is on something here and we could see it again that same feathering going in a direction of travel we have a transfer pattern with movement which is a swipe pattern there's blood on something and then we're just moving that in a direction usually when it's a white pattern we could see those original stains so the drawing and that someone tries to wipe them off with a cloth now we're looking at a cast-off pattern so this is a subcategory of spatter that's a projection mechanism so blood is on an object and we're moving that object in space that could be someone's hand that could be a pipe that could be a bat that could be a knife and as that object moves blood will be flung off it and we have these very distinct linear patterns or curvilinear patterns at a crime scene if we see these cast-off patterns they can go up the walls they can go across the floor and even onto the ceiling so we're looking at a spatter pattern but we have a normally continuous drops of blood that are being interrupted or blocked by something and that gives us a pattern what's called the void sometimes we have crime scenes where there's something important that would be in that pool or in that pattern or that spatter pattern and it's been removed so it could be someone's bag or a cell phone their wallet I had a crime scene where if someone was bludgeoned and adjacent to his head was the complete absence of blood spatter looking to the left of him there was a spatter pattern it didn't line up what we determined was that the curtains inside of the hotel room were open at the time of the crime and then closed later on we've gone over how these patterns are created are different categories of patterns and what we can interpret from these patterns at a crime scene this is not a simple process this stuff takes time training and experience and beyond that there's no absolutes with any of this there's no one specific answer then it's only that one answer I hope you guys learned a lot [Applause]

Channel: WIRED

Views: 8,690,025

Rating: 4.9488745 out of 5

Keywords: technique tutorial, crime scene, crime scene investigation, csi, bloodstains, bloodstain, bloodstain pattern, blood spatter, bloodspatter, analyzing blood stain, bloodstain analysis, blood stain analysis, blood stain, blood, matthew steiner, forensics, forensics expert, forensics expert breaks down, forensics bloodstain patterns, bloodstain break down, blood patterns, blood spatter pattern, wired technique tutorial, crime scene analysis, crime scene investigator, stain, wired

Id: 0jltioeaEyY

Length: 17min 7sec (1027 seconds)

Published: Thu Jan 30 2020

Reddit Comments

[u/Adam19135]

To Handlers - How do you paint a picture for your Agents at a crime scene? What interesting evidence have you left behind and how did your Agents follow up on it?

To Agents - What's the weirdest/scariest piece of evidence that you've found at a crime scene?

[u/blackd0nuts]

This is awesome! Also I suggest for every Handler to get the Forensic, Profiling and Serial Killers supplement from CoC which is a tremendous source of information regarding crime scenes and forensic from early 1900 to nowadays.