Blood Spatter Analysis Lecture - part 1

Summary

This lecture delves into the intricate field of blood spatter analysis, a crucial forensic technique. It covers how blood patterns reveal information about the crime, such as weapon type, number of blows, and victim position. The talk introduces various detection methods, including light sources, presumptive tests, and reagents like luminol and phenalene. It also explores the significance of blood spatter patterns, the physics of blood drop formation, and the use of trigonometry to determine angles of impact, ultimately helping to identify the crime's point of origin.

Takeaways

• 🔎 Blood Spatter Analysis (BSPA) examines patterns of blood stains to determine various aspects of a crime scene.
• 🚔 Forensic scientists can deduce information such as the type of weapon used, the speed of the weapon, the number of blows, and the position of the assailant and victim.
• 🕵️‍♂️ Different techniques are used to detect blood, including specific light sources and filters, presumptive tests, and reagents like phenalene and heem sticks.
• 💡 Luminol is a chemical that reacts with blood to create a blue glow, useful for revealing blood stains that are not visible to the naked eye.
• 🚫 Bleach can interfere with the detection process, as it reacts with certain chemicals used for blood detection, leaving a smudge instead of a glow.
• 💚 Florene is another chemical that can be used for detecting fine blood stains, causing them to glow greenish-white.
• 📸 Crystal Violet is used for creating a purple color in blood stains for photographic documentation, helping to identify shoe types and footprints.
• 🔍 Blood stain patterns are categorized by the force applied, such as low, medium, or high velocity spatters, and can indicate the direction of the blood flow.
• 📏 The size and shape of blood drops can provide information about the distance and angle of the blood drop, influenced by factors like the volume and the surface it falls on.
• 📐 Trigonometry is used to calculate the angle of impact from blood drops, with measurements of width and length plugged into a spreadsheet for precise calculations.
• 📍 The point of origin and area of origin can be determined by analyzing the pattern and direction of blood spatters, converging to the point where the incident occurred.

Q & A

What is the main focus of the lecture?

The lecture focuses on blood spatter, discussing the patterns that blood stains present on different surfaces and the techniques forensic scientists use to detect and analyze them.

What does BSPA stand for in the context of the lecture?

BSPA stands for Blood Stain Pattern Analysis, which is a method used by investigators to analyze the patterns of blood spatter at crime scenes.

What can forensic scientists deduce from blood spatter analysis?

Forensic scientists can deduce the type of weapon used, the speed of the weapon, the number of blows, the handedness of the assailant, the position of the victim, the sequence of wounds, the movement of the assailant, and the time of death from blood spatter analysis.

What are the different light sources that forensic scientists might use to detect blood?

Forensic scientists may use different light sources such as a flashlight with a particular filter or UV lights to make blood stains visible that are not visible to the naked eye.

What is a presumptive test in the context of blood detection?

A presumptive test is a chemical test that reacts with the properties of hemoglobin to indicate the presence of blood, but it does not confirm if the blood is human.

What is the purpose of using phenalene or a heem stick in blood detection?

Phenalene or a heem stick are reagents used to swab a surface; if blood is present, the swab turns pink, indicating the presence of blood.

What is the chemical luminol used for in blood detection?

Luminol is a chemical used in blood detection that glows blue when sprayed on a surface, revealing blood stains that are not visible under normal lighting conditions.

What is the difference between a transfer and a contact blood stain pattern?

A transfer blood stain pattern occurs when blood is wiped or smeared onto a surface, while a contact pattern is created by direct contact between the blood source and the surface.

What is stringing and how is it used in blood spatter analysis?

Stringing is a technique used in blood spatter analysis where a string is run through elliptical blood drops to determine the direction of the blood flow and to help identify the origin of the blood spatter.

How do forensic scientists determine the angle of impact from a blood drop?

Forensic scientists use trigonometry to measure the width and length of a blood drop, calculate the sine of the angle, and determine the angle of impact.

What is the significance of the point of convergence in blood spatter analysis?

The point of convergence is where lines drawn through the elliptical blood drops intersect, indicating the area or point of origin of the blood spatter, which helps in understanding the crime scene dynamics.

How does the height of a blood drop affect its size and the resulting spatter pattern?

The height from which a blood drop falls affects its speed and, consequently, its size and the diameter of the resulting spatter pattern. The higher the drop, the larger the diameter, until it reaches a maximum due to air resistance.

What factors influence the shape of a blood drop when it hits a surface?

The shape of a blood drop when it hits a surface is influenced by the volume of the drop, the speed at which it falls, and the type of surface it lands on, such as smooth glass or rough cardboard.

What is the significance of spines in blood drop analysis?

Spines are elongated extensions from the main drop that can indicate the height from which the drop fell and the type of surface it landed on, providing clues about the crime scene.

How do forensic scientists use the shape of blood drops to determine the direction of flow?

Forensic scientists look at the shape of blood drops, particularly the elongated droplets, to determine the direction of flow. The tail of the droplet points in the direction the blood was traveling when it fell.

Outlines

00:00

🔎 Introduction to Blood Spatter Analysis

The lecture introduces the concept of blood spatter analysis, a forensic science technique used to interpret patterns of blood stains on various surfaces. The abbreviation 'BSPA' stands for Blood Stain Pattern Analysis, which helps investigators deduce information such as the type of weapon used, the speed and number of blows, the position of the victim, and the sequence of events at a crime scene. The lecture also mentions the use of different light sources and presumptive tests to detect blood, including UV lights and reagents like phenalene, as well as the use of luminol to reveal blood presence through a blue glow. Additionally, the importance of understanding blood spatter patterns for determining the crime scene's location and the use of stringing or lasers to analyze the spatter's distribution are discussed.

05:01

📚 Understanding Blood Spatter Patterns and Techniques

This paragraph delves deeper into the types of blood spatter, including round and elongated drops, and the significance of these patterns in determining the direction of blood flow and the origin of the stains. The concept of 'spines' radiating from a parent drop and 'satellites' as smaller drops that break away are explained. The impact of factors like drop height, volume, and surface type on the formation of these patterns is discussed. The paragraph also covers the use of basic physics and trigonometry to calculate the angle of impact and the point of origin of the blood spatter. The importance of precise measurements in millimeters for accurate analysis is emphasized, and the process of using stringing or laser technology to find the area and point of origin at a crime scene is described.

10:01

📉 Advanced Blood Spatter Analysis: Point of Origin and Convergence

The final paragraph focuses on advanced techniques in blood spatter analysis, specifically the determination of the point of origin and point of convergence. It explains how CSIs use elliptical blood drops to draw lines that intersect at the area of origin, and how the point of convergence indicates the source of the blood spatter. The paragraph introduces the concept of using three-dimensional analysis, including height (Z-axis), to accurately pinpoint the origin. It also discusses the use of Excel spreadsheets with pre-populated formulas to assist with trigonometric calculations for determining angles of impact based on the width and length of blood drops. The importance of accurate measurements and the process of stringing to visualize the intersection points for origin determination are reiterated.

Keywords

💡Blood Spatter

Blood spatter refers to the pattern created by blood droplets when they impact a surface, which can be analyzed to determine the nature of the incident that caused the spattering. In the video, blood spatter is the central theme, as it is used to deduce information about the crime scene, such as the weapon used, the movement of the assailant, and the position of the victim.

💡BSPA

BSPA stands for Blood Stain Pattern Analysis, a forensic technique used to interpret the patterns of bloodstains to reconstruct the events of violent crimes. The script mentions BSPA as the abbreviation for this analysis, highlighting its importance in understanding the dynamics of the crime scene.

💡Forensic Scientists

Forensic scientists are professionals who apply scientific methods and techniques to investigate crimes. In the context of the video, forensic scientists are responsible for detecting and analyzing blood spatter at crime scenes, using various tools and tests to uncover evidence.

💡Presumptive Test

A presumptive test is a preliminary chemical test used to identify the presence of blood. The script describes how forensic scientists may use presumptive tests that react with hemoglobin, a component of blood, to indicate the presence of blood at a crime scene, although these tests do not confirm the blood is human.

💡Luminol

Luminol is a chemical used in forensic science to detect blood that has been cleaned up or is not visible to the naked eye. When sprayed on a surface, it reacts with iron in hemoglobin, causing it to glow blue, as illustrated in the video with the example of a couch where a body had been dragged.

💡Florene

Florene is another chemical used for detecting blood, especially fine stains and smears. It reacts with blood to produce a greenish-white glow, as mentioned in the script, and is useful for cases where other methods might not be as effective.

💡Crystal Violet

Crystal Violet is a chemical reagent used by forensic scientists to create a visible image of bloodstains, particularly when a photograph is needed. The script explains that after applying Crystal Violet, the stains turn purple, aiding in the identification of shoe prints and other evidence.

💡High-Velocity Spatters

High-velocity spatters are blood droplets that have been projected at high speeds, typically due to a forceful impact. The script discusses how the velocity of the spatter can indicate the force applied, which is crucial for reconstructing the events at the crime scene.

💡Transfer

A transfer in blood spatter analysis refers to blood that has been moved from its original location, often by contact with an object or person. The script mentions transfer as a category of blood spatter that can help forensic scientists understand how blood was spread at the crime scene.

💡Stringing

Stringing is a technique used to determine the point of origin in a crime scene by connecting the elongated ends of blood droplets. The script describes how forensic scientists use stringing, or more modernly lasers, to find where the blood originated from by seeing where the strings intersect.

💡Satellites

In blood spatter analysis, satellites are small blood droplets that break away from the main droplet, or parent drop, and impact another surface. The script explains that the presence of satellites can indicate the height from which the main droplet fell and the nature of the surface it impacted.

💡Trigonometry

Trigonometry is a branch of mathematics that deals with the relationships between the sides and angles of triangles. The script introduces the use of trigonometry to calculate the angle of impact in blood spatter analysis, which helps forensic scientists determine the trajectory of the blood droplets.

Highlights

Blood spatter analysis (BSPA) is used to determine patterns of blood stains on various surfaces.

Forensic scientists can deduce information such as the type of weapon used, weapon speed, number of blows, victim position, and handedness from blood spatter patterns.

Investigators can discern the sequence of wounds and the movement of the assailant around the victim through blood spatter.

Different drying times and immediate or delayed death can be inferred from the blood spatter at a crime scene.

Forensic tools such as specific light sources and filters can reveal blood stains not visible to the naked eye.

Presumptive tests react with hemoglobin properties but cannot confirm human blood without lab analysis.

Swabbing and reagent application, such as phenalene or a heem stick, can confirm the presence of blood with a color change.

Luminol is a chemical that reacts with blood to produce a blue glow, useful for detecting cleaned-up crime scenes.

Chemical reactions with substances like bleach can interfere with blood detection methods.

Florene is used for fine stains and smears, producing a greenish-white glow, but can also react with non-blood substances.

Crystal Violet is applied for photographic imaging of blood patterns, resulting in a purple coloration.

Different types of blood spatter patterns indicate the force and method of the crime, such as passive drops, projected stains, and transfer/contact stains.

Stringing or laser technology helps determine the crime scene by analyzing the positioning of blood spatter.

Elongated blood drops can indicate the direction of blood flow and the origin of the spatter.

Spines and satellite drops provide additional information about the height and force of the blood drop impact.

Basic physics principles, such as the relationship between drop speed and diameter, are applied in blood spatter analysis.

The volume and surface type affect the appearance of blood drops, influencing the analysis of spatter patterns.

Trigonometry is used to calculate the angle of impact from the dimensions of blood drops.

Excel programs can automate the trigonometric calculations for blood spatter analysis.

The point of origin and point of convergence are critical in determining the location and source of the crime.

Transcripts

welcome for this lecture we're going to

talk about blood spatter and we'll be

looking at different techniques uh 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 um 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 uh 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 um but we're going to call it

spatter um the type of weapon that was

used how fast that weapon was moving the

number of blows on a victim

whether the vi the asant was right or

left-handed how he was position he or

she was positioned over the victim um

they can also tell which wounds happened

first um how the as salent 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 scientist at a crime

scene CSI will use different types of

sources to detect if the evidence you

may have seen this on different TV shows

so they could use a different light

source um something as simple as a

flashlight with a particular filter on

it um so it may not be visible to the

naked eye but the uh 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 youve probably seen this

where on different shows they will swab

something and then apply a different

type of reagent uh phenalene is an

example of that um or a heem 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 this

is 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 um or the lights dimmed 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 they if it has been cleaned up

especially with bleach it will react so

we can see here since it's entire smudge

this particular area was cleaned with a

chemical

um another type of chemical that they

can apply these are for fine stains

smears and this will glow a greenish

white and this is

florene um so it works similar to

luminol but again it can react with

other things like copper and

bleach there is a another um Crystal

Violet lco Crystal Violet and they will

use this if they need a photog graph an

image so as we progress we can see

different Footprints and by the time

they apply it'll be a purple color

violet um they can actually see the type

or make of the shoe by the time they

finish processing it now 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 pulls

a projected blood stain there would be a

a particular Force applied and they will

say that that's low medium or High

Velocity spatters depending on um the

force that's uh 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 wiped

then it would be categorized as this

okay if it's a blood spattered

but to fall into this definition sorry

um it's just a random distribution of

the stains and it can vary in shape and

size and fenic scientists will use this

to determine where the crime took place

um and we'll do something like this in

class in our lab and and they refer to

it as stringing now we're going to use a

stringing but nowadays they will use

lasers um it kind of speeds up the

process of um processing the crime scene

so they can tell how much blood the

force just by the positioning of the

blood

spatter so we can see here these are

different types of spatters uh 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 uh 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 bad 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 um 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 then I already

mentioned the spines that would help

radiate and this would indicate if it's

a large drop and the spines are

projected away from that parent drop

then it's up higher um is where it fell

from okay so when you determine the

distance uh some basic physics come into

play the faster the drop the larger D

diameter so height would play a factor

in that now anytime you get above 7t

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 a b

even though it would fall from a greater

distance so those are two factors you

need to keep into mind when you're

looking at drops another thing you need

to look at is the type of surface so

here um 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 track

traveling so I like this little saying

here that the 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° straight

to the ground um 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 math

um mathematical equations that's what

computers are for but I did want to

introduce this to you they do use trig

to determine um 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 AIS 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° and the ratio is

0.4 um 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 as usually where

that takes place okay I kind of thrown

out a point of origin area of origin so

I can can look at the crime scene or

actually CSI would look at a crime scene

and these are the elliptical blood trops

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 okay so where it

converges um is very similar to the area

of origin but the point of converion

will dictate The Source okay 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 um and so you would look at all

the different blood spatters

now this is just a two-dimensional and

so the Y AIS 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' mentioned stringing so

this is an example down here so they've

taken the drops run the string or the

line through the

elliptical um and then where they all

intersect on all these different drops

on the wall would be the point of

origin