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 illegal 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
[Music]
for us at crime scenes when we
investigate them safety is number one
we want to protect ourselves i think we
various bloodborne pathogens that we're
dealing with and
secondly we don't want to contaminate
the crime scene so we don't want the
harrison fibers
on ourselves the dna that's shedding off
of us falling onto our evidence
at a crime scene we'd wear multiple
layers of gloves if we're going to 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 a
really good look
for talking on camera next we're going
to talk about the three main categories
of blood stains that we can encounter at
a crime scene
[Music]
today we're going to be using
defibrinated 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 blood same pattern analysts
correlate the appearance of these blood
same 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 prime 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 blood
scenes 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 without
any sort of outside external force other
than gravity or contact so we're going
to 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 sphere of blood strikes the
surface at 90 degrees
we have a very even round
circle at a crime scene but also what
affects the way our blood stain looks
is the surface itself we have plexiglass
and we notice that the edge
characteristics of our blood stain
are very even now that we observe 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 scalping is just the 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 the surface to a
rougher surface wood
so we can see a vast difference from
where we started where we have smooth
edge characteristics
now we have this spinier 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 a parent stain so
this main stain here is my parent 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 going to be looking at
contact transfer stance 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 suspect's 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 suspect's shoe wear
impression we're gonna coat the bottom
of the shoe and we're gonna transfer the
pattern
of the bottom of the shoe to our clean
surface so 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 with our naked eye we could
find later on with chemicals like
luminol or 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 going
to take some blood
saturate a portion of our genes with it
and we're going to transfer
that onto our surface so sometimes in
real crime scenes these get
misinterpreted
as the lines of maneuvering your
fingerprints or palm print we would see
is that
unlike fingerprints are just straight
lines either way we would document this
and collect it in sensor lab
and then under magnification analyze it
so next we're going to discuss how
movement could affect these transfer
stain patterns so i'm going to take some
blood and put it onto my hand
and then move that across the surface so
if i touch the surface
and then move my hand we see what's
called feathering the effect of movement
on blood
just like if i took a paintbrush and
moved it across a wall
in the beginning would be darker but
eventually it would get lighter so
this feathering effect helps us
interpret movement at a crime scene
this could be found at a crime scene in
many different ways
one could be a 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
are 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 through
the scene and we'd see the same effect
that feathering going towards the body
next we're going to cover 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 a
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 were
laying down we'd see a different flow
pattern so next we're going to discuss
saturation and pooling patterns that we
have at a crime scene saturation and
pulling patterns
could tell us that someone is bleeding
in 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 expirated pattern or a pattern that's
coming from
an 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 has 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 then 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 that we're looking at
just the accumulation of blood but
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 affect
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 bloodstain
pattern analysis with this category of
blood stains we're looking at some sort
of external force
on an open source of blood so i'm going
to do is going to put a small amount of
blood on her wood here
i'm going to strike it with a hammer and
what we should see is an impact spatter
on the plexiglass in front of us put on
my goggles i'm going to put my hood up
and give us a small amount of blood here
all right ready
there we go so as you can see
not only do we have impact spatter on
the plexiglass in front of us
we also have it on our suspect here okay
so we applied
force to an open source of blood and we
have a resulting impact
stain our stain pattern what we'll
notice is directly opposite where the
force was applied
we have our blood striking that surface
at 90 degrees so these stains that we
have right here near the bottom
are circular but the further we move
away from that
source these blood stains 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 a 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 backspatter
first off we started by creating
different patterns that we could analyze
next step we're going to 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 the 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 going to 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 going to 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
stainless going
so then i'll move around the pattern
from different sides of it
and draw through different stains uh 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
stains towards the inside this is the
perfect opportunity for us
to do some analysis i could keep going
and
draw more lines for 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 going to 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 arc sine 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 sub millimeter 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
stand
that's 1.7 millimeters we're going to
divide
3.1 into 1.7 so if we
do the arc sine of that number that will
give us the angle of impact which is
33.25
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
it is two millimeters so we would divide
four into two which gives us 0.5
and the arc sine of 0.5 is 30 degrees
and we can see it's 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 converges 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
going to 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 feel it's 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 going to try
something a little more difficult
interpreting relationships
[Music]
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 of 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 drip pattern this could be the
victim's blood
this could be the suspect's 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 moved
through it
so we could see from our discussion
earlier feathering
that the directionality is coming
towards me something is passively
dripping
blood it could be a weapon that could be
a victim it 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 again that same feathering
going in the 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
they're drying and then 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 curvy linear 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 a 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 someone was
bludgeoned
and adjacent to his head was
the complete absence of a 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 our 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 experience
and beyond that it 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]