3 - 10 - Week 3B - 4 Blood Spatter Analysis (08 17), kryminalistyka, introduction to forensic science
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[MUSIC]So, we've talked about blood biochemistryand how we can use blood biochemistryto determinewhere blood comes from, and who it belongs to.So now let's talk about some blood physics andsee if we can work out how the blood got there.So what we're going to do is take a lookat some blood patterns,and see if we can reconstruct the crimefrom the pattern of the blood.So if there is blood on the suspect, fromlooking at howthe blood is distributed, can weunderstand how the crime was committed?The technical term for this distributionof the blood onthe suspect in the crime scene is calledblood spatter,so what we're going to do is blood spatteranalysis.So, here are some typical marks in bloodthat might be found at a crime scene.Both of these marks come from the transferof blood.So in this case, blood has got on anobjectand then has been transferred to the placewhere it's found.So the one on the left, for instance,clearly someone hasstepped in blood, and this is a partialbloody foot print.The one on the right is a hand print inblood.Someone has got blood on their hand, andtheir hand iscovered in blood, and then it's beensmeared on the wall here.The pattern, the way that the blood isdistributed, can tellyou about where the blood came from andhow it got there.So if in a violent crime an artery issevered,then there will be a very characteristicpattern of arterial spurting.So, because arteries come directly fromtheheart, the pressure in the artery variesas the heart beats, and this means thatblood will spurt from the artery.So instead of a continuous flow, you willget a spurt with eachheartbeat, and this gives a splash ofblood, in this case, on the wall.And because it's a relatively large amountof blood comingfrom the artery, it will then dribble downthe wall.This is called arterial spurting.On the other hand, if someone has a muchsmaller wound,and for instance, is standing therewondering what todo, then you will get a pattern of blooddrips.Now, the exact pattern will depend on thesurface in question,and also how long the person stands therewith blood dripping into the pool.The pattern created by flying blood willalso depend onthe violence of the event that caused thatblood to fly.If it's a relatively low energy event, forinstance, anordinary fight, then you will get lowvelocity blood spatter.This can also be from blood that isfallingfrom a wound, and also blood that is cast off.For instance, if someone is struck with aweapon and the assailantthen pulls the weapon back to take asecond blow, as hepulls the weapon back, there will be someblood drops cast offfrom the weapon, and these would also giveyou low velocity blood spatter.Thinking about someone being attacked by aweapon,for instance, being beaten with a baseballbat,this is a relatively energetic event.The blood that's flying around will movesomewhat faster, and thiswill give medium velocity spatter as shownin the picture here.The most energetic events would, forinstance, be associated with gun shots,and this gives high velocity bloodspatter, where you have a lotof small droplets of blood moving veryfast, a little bit like a mist.So this is high velocity blood spatter.So by looking at these patterns of blood,the forensicscientist can determine something aboutwhat happened in the crime.Now, let's consider a falling drop ofblood.A blood drop, as it falls, is roughlyspherical.And if it hits the floor at an angle of90 degrees, then you will get a circularblood spatter mark.But suppose that drop of blood doesn't hitthe floor at 90 degrees,suppose it hits the floor at an angle,then you will not get a circular patternon the floor,you'll get this elongated shape.And maybe, if the blood, as it hits thefloor, has enough energy, there will be alittle splash.So in front of the main elongated shape,there will be alittle extra dot of blood that bouncedout from the main droplet.So for instance, you may have a patternlike this.So here the blood has come from the left,because you cansee the main shape followed by a smallerdroplet on the right.In fact, we can correlate the shape oftheseblood droplets with the angle at whichthey hit the surface.So when you have a 90 degree angle, weget this circular pattern,and as you go through to a very acuteangle, it becomes more and more elongated.So with a very acute angle of tendegrees, you get this very long blooddroplet shape.[BLANK_AUDIO]Now, suppose at the crime scene youhave multiple blood droplets in differentplaces.We can work out which point in space wasthe originof those blood droplets by plotting linesbackwards from the droplets.Where all of the lines cross, which iscalled the point of convergence,this would have been the source of theblood.Now when we look at a diagram like this intwo dimensions,it looks very simple, but of course, crimesoccur in three dimensions.So, we have to do this kind of bloodspatter analysis in three dimensions.So if we can plot the lines back from thebloodstains, for instance, on thewall to a point of convergence, then weknow in three dimensional space wherethe crime happened.So in this example for instance,plotting the lines back from the bloodstain pattern on the wall gives us theheight above the floor at which thisevent that generated the blood happened.So if that height above the floor issay, five feet,then we'd know the victim was stillstanding at the time.If that height above the floor is only afew inches, then of course,we know the victim was already on thefloor when they were being beaten.And this is very important evidence forreconstructing the crime scene.Now of course, these diagrams we're usinghere are very, very simplified.And in a real situation, it would actually bemuch more complicated to work out thepoint of convergence.In fact, if you have a crime scene witheven more blood than this, it may just beimpossiblebecause there's just too much blood at thecrime scene to be able to interpret thesituation.[BLANK_AUDIO] [ Pobierz całość w formacie PDF ]
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[MUSIC]So, we've talked about blood biochemistryand how we can use blood biochemistryto determinewhere blood comes from, and who it belongs to.So now let's talk about some blood physics andsee if we can work out how the blood got there.So what we're going to do is take a lookat some blood patterns,and see if we can reconstruct the crimefrom the pattern of the blood.So if there is blood on the suspect, fromlooking at howthe blood is distributed, can weunderstand how the crime was committed?The technical term for this distributionof the blood onthe suspect in the crime scene is calledblood spatter,so what we're going to do is blood spatteranalysis.So, here are some typical marks in bloodthat might be found at a crime scene.Both of these marks come from the transferof blood.So in this case, blood has got on anobjectand then has been transferred to the placewhere it's found.So the one on the left, for instance,clearly someone hasstepped in blood, and this is a partialbloody foot print.The one on the right is a hand print inblood.Someone has got blood on their hand, andtheir hand iscovered in blood, and then it's beensmeared on the wall here.The pattern, the way that the blood isdistributed, can tellyou about where the blood came from andhow it got there.So if in a violent crime an artery issevered,then there will be a very characteristicpattern of arterial spurting.So, because arteries come directly fromtheheart, the pressure in the artery variesas the heart beats, and this means thatblood will spurt from the artery.So instead of a continuous flow, you willget a spurt with eachheartbeat, and this gives a splash ofblood, in this case, on the wall.And because it's a relatively large amountof blood comingfrom the artery, it will then dribble downthe wall.This is called arterial spurting.On the other hand, if someone has a muchsmaller wound,and for instance, is standing therewondering what todo, then you will get a pattern of blooddrips.Now, the exact pattern will depend on thesurface in question,and also how long the person stands therewith blood dripping into the pool.The pattern created by flying blood willalso depend onthe violence of the event that caused thatblood to fly.If it's a relatively low energy event, forinstance, anordinary fight, then you will get lowvelocity blood spatter.This can also be from blood that isfallingfrom a wound, and also blood that is cast off.For instance, if someone is struck with aweapon and the assailantthen pulls the weapon back to take asecond blow, as hepulls the weapon back, there will be someblood drops cast offfrom the weapon, and these would also giveyou low velocity blood spatter.Thinking about someone being attacked by aweapon,for instance, being beaten with a baseballbat,this is a relatively energetic event.The blood that's flying around will movesomewhat faster, and thiswill give medium velocity spatter as shownin the picture here.The most energetic events would, forinstance, be associated with gun shots,and this gives high velocity bloodspatter, where you have a lotof small droplets of blood moving veryfast, a little bit like a mist.So this is high velocity blood spatter.So by looking at these patterns of blood,the forensicscientist can determine something aboutwhat happened in the crime.Now, let's consider a falling drop ofblood.A blood drop, as it falls, is roughlyspherical.And if it hits the floor at an angle of90 degrees, then you will get a circularblood spatter mark.But suppose that drop of blood doesn't hitthe floor at 90 degrees,suppose it hits the floor at an angle,then you will not get a circular patternon the floor,you'll get this elongated shape.And maybe, if the blood, as it hits thefloor, has enough energy, there will be alittle splash.So in front of the main elongated shape,there will be alittle extra dot of blood that bouncedout from the main droplet.So for instance, you may have a patternlike this.So here the blood has come from the left,because you cansee the main shape followed by a smallerdroplet on the right.In fact, we can correlate the shape oftheseblood droplets with the angle at whichthey hit the surface.So when you have a 90 degree angle, weget this circular pattern,and as you go through to a very acuteangle, it becomes more and more elongated.So with a very acute angle of tendegrees, you get this very long blooddroplet shape.[BLANK_AUDIO]Now, suppose at the crime scene youhave multiple blood droplets in differentplaces.We can work out which point in space wasthe originof those blood droplets by plotting linesbackwards from the droplets.Where all of the lines cross, which iscalled the point of convergence,this would have been the source of theblood.Now when we look at a diagram like this intwo dimensions,it looks very simple, but of course, crimesoccur in three dimensions.So, we have to do this kind of bloodspatter analysis in three dimensions.So if we can plot the lines back from thebloodstains, for instance, on thewall to a point of convergence, then weknow in three dimensional space wherethe crime happened.So in this example for instance,plotting the lines back from the bloodstain pattern on the wall gives us theheight above the floor at which thisevent that generated the blood happened.So if that height above the floor issay, five feet,then we'd know the victim was stillstanding at the time.If that height above the floor is only afew inches, then of course,we know the victim was already on thefloor when they were being beaten.And this is very important evidence forreconstructing the crime scene.Now of course, these diagrams we're usinghere are very, very simplified.And in a real situation, it would actually bemuch more complicated to work out thepoint of convergence.In fact, if you have a crime scene witheven more blood than this, it may just beimpossiblebecause there's just too much blood at thecrime scene to be able to interpret thesituation.[BLANK_AUDIO] [ Pobierz całość w formacie PDF ]