BLOOD SPATTER ANALYSIS
Terms in this set (78)
blood spatter analysis was adopted in practical manner in US after what court case?
1954 Sheppard case
blood spatter analysis can provide what information?
-who shed blood?
-how did it get where it was found?
-what was the sequence of events that led to this pattern?
-origin of blood stain
-type of instrument causing stain
-direction from which it struck victim
-relative position of victim/assailant
-# of blows/gun shots
-truthfulness of suspects/witnesses
what is blood held together by?
cohesive forces that produce a surface resistant to penetration or separation
before a drop of blood can fall, what needs to happen?
gravitational attraction for the drop must exceed surface tension
*surface tension is broken w/ energy
shape and size of blood drop depends on what four factors?
size of drop
type of surface hit
how fast does a drop of blood fall?
increases speed as it falls until it hits terminal velocity (25 ft/ second)
when a drop of blood strikes at a right angle, spatter pattern forms what shape?
even circle around point of impact
when a drop of blood strikes at a smaller angle than 90 degrees, what shape does it create?
oval pattern w/ narrow/pointed end aiming in direction of travel
these surfaces create small patterns of blood spatter
smooth surfaces like glass, tile, and marble
when a drop of blood falls onto a hard surface, what can happen to the drops?
small secondary/satellite droplet may surround initial circular stain
with drops that hit smooth surfaces at less than 90 degrees- secondary stains are elongated but tails of satellite droplets point which direction?
point where they came from (NOT direction they are traveling)
spatters can be produced by what mechanisms?
slant at which blood drops strike surface
course the blood drop followed
how is impact angle determined?
using blood stain's width to length ratio
what is directionality used for?
used to make point of convergence and point of origin determinations
point of convergence
2d representation of the point where lines tracking the pathways of 2 or more spatters meet
at the scene, strings are attached from each stain according to direction of impact...where strings meet equal the
point of convergence
point of origin
3d representation of the point where lines tracking, not only the pathways, but also angles of impact of 2 or more spatters meet
what does the point of origin indicate?
general spatial location of blood source
absence of blood spatter in area you'd otherwise expect it
*could show where attacker was standing b/c body prevents blood from spattering behind it
you can classify projected spatter two different ways:
type of spatter
*both are useful due to overlapping in many areas
impact spatters occur in what type of situation?
*foreign object impacts victim
in what situation would one see projection spatter?
result from arterial bleeding, cast-off blood, and expirated blood
include both impact and projection spatter
what is an example of a scenario where you would see combination spatter?
victim is stabbed in chest or neck - see impact spatter from force of attack and projection spatter from arterial bleeding, expirated, or cast-off blood
classification by velocity looks at not only the velocity at which the impacting object strikes the blood source but also...
the velocity at which blood leaves the blood source when struck
classification by velocity divides into what different categories?
low, medium, and high velocity
the different velocity categories give an indication of what?
the object and mechanism used to make the spatter
this type of spatter occurs when an object traveling less than 5 ft/second strikes a surface
low velocity spatter
what would the spatter typically look like/size in low velocity spatter?
fairly large spatter - greater than 4mm
low velocity spatter is produce by what type of mechanisms?
drops dripping from wound or blood-soaked clothing or weapons
an arterial bleed would produce what type of pattern?
freely spurting artery results in linear and cascading spatter pattern
as the victim loses blood with an arterial bleed, what will happen to the pattern?
pattern's distance from wound, length, and volume may decline steadily as victim loses blood volume and pressure
blood flung from an object due to centrifugal force
when is cast-off blood typically seen?
when attacker uses weapon to deliver series of arcing blows
where is cast-off blood typically seen?
walls and ceilings
cast-off blood pattern tends to be a uniform trail of droplets which reflect...
arc in which object traveled
number of cast-off patterns indicates
minimum number of blows to the victim
*could be more but never less
determining point of convergence and angle of impact of cast-off stains can reveal what about the assailant?
assailant's position at the time weapon was swung
can you estimate the height and hand which delivered the blow?
in some cases
this type of spatter occurs from objects moving between 5 and 100ft/second
medium velocity spatter
what sizes are medium velocity spatter typically?
smaller than low velocity (1-4mm)
medium velocity spatter is created by what mechanisms?
impacts with blunt or sharp objects and possibly expirated blood
spatter from this type of object distributes blood in all directions from area of impact
analysis of directionality and impact angle of stains can help determine this
point of origin
this type of spatter results from an object striking victim at speed faster than 100ft/second or from expirated blood
average size of high velocity spatter
less than 1mm - mist like stains
most high velocity spatter is associated with this type of mechanism
gunshots - appearing near entrance and exit wounds
*w/ gunshot wounds, fine spatters behave differently depending on whether bullet is entering or exiting body
back spatter/blow back
blood stain associated with entrance wound
with back spatter, droplets travel in what direction?
droplets travel in opposite direction of path of bullet
back spatter is often found where?
on shooter or weapon
if very close range, back spatter may be found where?
in barrel of gun
high velocity spatter found at exit wound
blood droplets of forward spatter follow which direction?
direction of bullet
blood stain pattern resulting from when an object soaked in blood comes in contact with unstained object
what are some examples of transfer patterns?
bloody fingerprints, shoe prints, etc.
pattern created when a volume of blood in excess of 1mL strikes a surface at a low to medium velocity
the transfer of blood onto a target surface by a bloody object that is usually moving laterally
a surface where blood ends up
pattern created when a secondary target moves through an existing wet blood stain on some other object
the angle at which a blood droplet strikes a surface
angle of impact
a large pattern of blood that is created when blood escapes an artery under pressure; the increase and decrease in blood pressure is apparent
large patterns created under pressure, but with less volume and usually more distinctive evidence of blood pressure rising and falling
a mass of blood and other contaminants caused through clotting mechanisms
blood that hs been thrown from a secondary object onto a target other than the impact site
characteristic patterns present when blood drips into standing, wet blood
blodo which is spattered on to a target, as a result of breathing: typically, this occurs when an injury is sustained to the throat, mouth, or airway
usually the point on he body that received the blow or applied force, from which the blood was shed
the point in space where the blood spatter came from
the droplet from which satellite spatter originated
blood under pressure that strikes a target
small drops of blood that break of from the parent spatter when the parent droplet strikes a target surface
a pattern that helps to place an object or body in the scene: normally the area in question lacks blood even though areas surrounding it show blood
pattern left when an object moves through a partially dried stain, removing part of the blood, but leaving the outline of the stain intact
blood stains created from the application of the force or energy to the area where the blood is
pointed edges of a stain that radiate out to form the spatter