Welcome. For this lecture, we're going to talk about blood spatter, and we'll be looking at different techniques, what forensic scientists use to detect blood, and some of this we'll actually do in our labs. So go ahead and get out your lecture notes, your spiral. Okay, when we talk about blood spatter, it is looking at the patterns that blood stains will present itself on different types of surfaces.
So you'll see the abbreviation BSPA and different forms of that, but that stands for blood stain pattern analysis. So what an investigator will learn from the analysis of different blood spatter, and you may even see it splatter, but we're going to call it spatter, the type of weapon that was used, how fast that weapon was moving, the number of blows on a victim, whether the... assailant was right or left-handed, how he or she was positioned over the victim.
They can also tell which wounds happened first, how the assailant would move around the victim, type of injuries. They can even look on how long it was going, depending on how it dried in on the surface and whether the death was immediate or delayed. So forensic scientists at a crime scene CSIs will use different types of sources to detect the evidence. You may have seen this on different TV shows.
So they could use a different light source, something as simple as a flashlight with a particular filter on it. So it may not be visible to the naked eye, but the particular filter and UV lights can detect that. They may also use something called presumptive test and these would react with different properties of hemoglobin and there's different types, but it does not detect if it's human or not. So they would have to take that back to the lab to determine that.
But if blood is present, then you've probably seen this on shows, they will swab something and then apply a different type of reagent. Phenolphthalein is an example of that, or a heme stick. And if it turns pink, then, and they always make that a big drama. then blood is present.
I know you've heard of this, it's called luminol and it will glow blue and this is an example. So they just by spraying this of course it has to be pitch black or the lights dim. We can see here on the couch that there was a blue stain and then the body was drug across the room. Now one of the bad things that if it has been cleaned up especially with bleach it will react.
So we can see here since it's an entire smudge This particular area was cleaned with a chemical. Another type of chemical that we can apply, these are for fine stain smears, and this will glow a greenish white and this is fluorescein, so it works similar to luminol, but again it can react with other things like copper and bleach. There is another Crystal violet, leukocrystal violet, and they will use this if they need to photograph an image. So as we progress, we can see different footprints.
And by the time they apply, it will be a purple color, violet. They can actually see the type or make of the shoe by the time they finish processing it. And there are different types of patterns depending on the weapon and the method. So anything that's passive, this is due to gravity.
So these are drops off of a weapon, any kind of flow pattern from a wound, or anything that pools. A projected blood stain, there would be a particular force applied. And they will say that that's low, medium, or high velocity spatters, depending on the force that's placed behind it. Then you can also have a transfer or a contact.
So this would be if a weapon or if someone walks through. If it's white, then it would be categorized as this. Okay, if it's a blood spatter, to fall into this definition, sorry, it's just a random distribution of the stains, and it can vary in shape and size.
And forensic scientists will use this to determine where the crime took place. And we'll do something like this in class in our lab, and they refer to it as stringing. Now we're going to use a straining, but nowadays they will use lasers.
It kind of speeds up the process of processing the crime scene. So they can tell how much blood to force just by the positioning of the blood spatter. So what you see here, these are different types of spatters. We have a round, and these are little satellites. We'll talk about that in a second.
And more elongated, and they use these elongated spots or blood drops to determine the direction of the flow. So the origin or source is where it came from, where it originated from. So an example would be like a bat if that was used as a weapon. The angle, and this is where they would use the elongated drops. Now, I mentioned something about spines, kind of how it radiates out.
So this would be the parent drop, and it would then form spines going out. The higher the drop gets, the more spines there are. So if it's real close to the ground, then it would be more uniform. Another thing that would cause or not cause the spines would be the type of surface that it falls on.
Then anything that drops away from the parent is called a satellite. So these are small drops that would break away and hit another surface. And I already mentioned the spines that would help radiate. This would indicate if it's a large drop and the spines are projected away from that parent drop, then it's up higher is where it fell from.
Okay, so when you determine the distance, some basic physics come into play. The faster the drop, the larger the diameter. So height would play a factor in that. Now, anytime you get above seven feet, that's kind of where the speed will max out, and it's due to air resistance. Now, we're not going to do any calculations with that, but that's just something to keep in mind.
Now, the drop of the blood, how large it is, depends on the volume. So, for example, if it falls from a needle, something very small, obviously the volume is not going to be as great as if it comes from a bat, even though it would fall from a greater distance. So those are two factors you need to consider. keep in mind when you're looking at drops. Another thing you need to look at is the type of surface.
So here, a nice clean line around the perimeter. There's not many spines going off like it is here. So if it's a very smooth surface like glass, then it won't have the spines going off.
If it falls on wood or even some kind of a rough surface like cardboard, then you can notice the spines direct out. Now carpet's a little tricky because of the pile. that it would actually absorb the spot even though it would be the same volume as these three images at top okay we talked about or i mentioned about the direction they can tell from the angle so what they will do and we'll help we will use this when we're stringing or if we had the technology we would have lasers but it always points to the direction that it was traveling so i like this little saying here that Tail tells the tail.
And when they're referring to the tail, they are talking about the direction or these droplets that are elongated. Now, if it's dropped straight down, like, for example, if someone's walking rather slow and they have a weapon in their hand and it's dropping off, that's a 90 degree straight to the ground. When we start seeing the elliptical, so make sure you know it's either round or elliptical, that would be on the degrees.
And I have a really good visual coming up here in just a second on one weapon, one point of origin, and how the spatter can change on how that weapon is swung through the room. Now, we'll do something, a variation of this. We're not going to do any mathematical equations. That's what computers are for. But I do want to introduce this to you.
They do use trig to determine the angle of the impact. So they can take a blood drop and they can measure the width and the length and find the sign. And then the arc sign, they can then determine the angle or the percent.
So we have a program in Excel and it will do the calculations. So the formula is already plugged in. So when we're talking about the width and length, so you need to know this in order to do the measurements to plug it into the spreadsheet. So the width is always the narrow part and the length is the longest part of the drop.
So it's very easy to tell here, but you would need to measure in millimeters and be very precise when determining the width and the length, because that will affect the mathematical calculation, so be aware of that. So we're going to plug this into, like I said, the spreadsheet, and if it follows a curve, so if I look at my graph here, I can see that on the y-axis, I have the width and length ratio, and then along the bottom, I have the degrees. So as the degrees, if I am about 22 degrees and the ratio is point four and as I move up on the impact, so as I become more of a rounded rather as an elliptical shape, then I can see it would follow this path.
It would have a particular trend. Anything that diverges off of that, I would go back and take a look at my measurements is usually where that takes place. Okay, I've kind of thrown out a point of origin, area of origin, so I can look at the crime scene or actually CSI would look at a crime scene and These are the elliptical blood drops, and they would draw a line through it and string.
That's where stringing comes from, or a laser. And where they intersect would be the area of origin. So where it converges is very similar to the area of origin, but the point of conversion will dictate the source. So you would have possibly different areas of blood splatter, maybe on one wall, ceiling.
two different walls. So they would take the point or the origin, the area of origin, and then they would look at both areas on either wall, and then they can bring it back to the point of convergence. So in the lab, it's going to be referring to three different points, and so you would look at all the different blood spatters. Now this is just a two-dimensional.
and so the y-axis and the x-axis and where those lines meet or intersect is the point of convergence down here. And we're also going to factor in z, how high off the ground, the height of the drops. Okay, so I've mentioned stringing, so this is an example down here.
So they've taken the drops, run the string or the line through the elliptical, and then where they all intersect on all these different drops on the wall would be the point of convergence. point of origin.