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forensic sci > lec 9 bloodstains > Flashcards

lec 9 bloodstains Flashcards

1
Q

crime-scene reconstruction

A

-method used to support a likely sequence of events at a crime
scene
-observation, evaluation of physical evidence, statements made by ppl involved

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2
Q

satellite stain

A

A smaller bloodstain that originated during the formation of the
parent stain as a result of blood impacting a surface

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3
Q

angle of impact

A

angle at which a blood droplet strikes a surface

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4
Q

spatter pattern

A

A bloodstain resulting from an airborne blood drop created when
external force is applied to liquid
blood

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5
Q

impact spatter

A

A bloodstain pattern resulting from
an object striking liquid blood.

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6
Q

forward spatter

A

A bloodstain pattern resulting from
blood drops that can be produced
when a projectile creates an exit
wound.

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7
Q

backspatter

A

bloodstain pattern resulting from blood drops that can be produced when a projectile creates an
entrance wound.

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8
Q

area of convergence

A

area containing the intersections generated by lines drawn through the long axes of individual stains that indicates in two dimensions the location of the blood source

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9
Q

area of origin

A

space in three dimensions to which the trajectories of spatter can be utilized to determine the location of the spatter-producing event

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10
Q

cast-off

A

bloodstain pattern that is created when blood is flung from a bloodbearing object in motion onto a surface.

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11
Q

projected pattern

A

bloodstain pattern
-ejection of blood under hydraulic pressure, typically from breach in circulatory system

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12
Q

expiration pattern

A

A bloodstain pattern resulting from
blood forced by airflow out of the
nose, mouth, or a wound.

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13
Q

void

A

An absence of blood in an otherwise continuous bloodstain or
bloodstain pattern.

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14
Q

transfer stain

A

A bloodstain resulting from contact
between a blood-bearing surface
and another surface.

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15
Q

flow

A

A bloodstain resulting from the
movement of a volume of blood on
a surface due to gravity or movement of the target.

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16
Q

perimeter stain

A

An altered stain consisting of its
edge characteristics, the central
area having been partially or
entirely removed.

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17
Q

the intersection of straight lines through the long axis of several individual bloodstains in an impact splatter pattern illustrates the ______ of the pattern

A

area of convergence

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18
Q

the pointed end of a bloodstain always faces

A

its direction of travel

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19
Q

the amount of splatter from a blood droplet falling on a hard, nonporous surface is _______ that of a drop of blood of equal size, falling from the same distance onto a softer, porous surface

A

greater than

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20
Q

crime-scene reconstruction requires piecing together…?

A

-accounts given by witnesses and suspects
-input from medical examiner
-the story told by evidence recovered at the crime scene

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21
Q

when an object blocs the deposition of blood spatter onto a target surface or object the result is a…?

A

void pattern

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22
Q

physical evidence that can be used to aid in a crime-scene reconstruction includes..?
a. blood spatter
b. gunshot residue
c. glass fragments
d. all of the above

A

d. all of the above

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23
Q

the most common type of bloodstain pattern found at a crime scene is..?

A

impact splatter

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24
Q

drops propelled from a blunt surface will be larger and the pattern will be
a. narrow
b. wide
c. linear
d. thin

25
what is created when an object with blood on it touches one that does not have blood on it?
transfer pattern
26
at the crime scene, the string method is used to find the ____ of an impact splatter pattern
area of origin
27
what is the composition of whole blood? explain each element
-plasma 55% (solutes, protien, water) -buffy coat 1% (platelets, leukocytes) -RBCs 44% (ethereyoctes)
28
what component of blood is responsible for clotting?
platelets
29
what are some important fluid properties of blood that are important to blood pattern analysis?
Density, surface tension, viscosity, and packed cell volume (PCV%)
30
what does ex-vivo mean?
outside of body
31
briefly explain surface tension and packed cell volume properties of blood?
surface tension: how the molecules in blood react with each other packed cell volume (PCV): how blood with flow or dry, affected by water and alcohol
32
define Bloodstain pattern analysis (BPA)
study of the size, shape, and distribution of bloodstains to determine the physical events which gave rise to their origin
33
what are the 3 bloodstain mechanisms? with examples
passive -no force applied -drip stains, patterns, trails transfer -transfer stains, wipes, swipes motion -impact patterns, cast-off patterns, expirated patterns(exhaled)
34
what are the three types of drips?
drip stain, drip pattern, drip trail
35
drip stain
bloodstain resulting from a falling drop that formed due to gravity
36
drip pattern
bloodstain pattern resulting from a liquid that was dripped into another liquid, at least one of which was blood
37
drip trail
bloodstain pattern resulting from the movement of a source of drip stains between two points
38
explain parent and satellite stains
parent stains are the original, bigger stain whereas satellite stains are smaller stains caused by the impact of the droplet with the surface
39
what is the effect of height on drip stains?
height of the blood source from the substrate increases, the diameter of the bloodstain also increases
40
!!!!explain the effect of angle on drip stains
the smaller the angle, the more elongated the drip will be
41
what is a factor that can impact a bloodstain pattern?
surface/ substrate -porus/nonporous -absorbent/not -smooth/layered
42
explain environmental effects and challenges for BPA
snow -type of snow affects how much the blood travels - ex. powder snow can absorb, crust can act like hard surface -can also dilute blood grass -can be absorbant -layered, so blood does not create clean drip
43
what are two spatter patterns? explain them
Cast-off -blood is flung or projected from an object in motion or one that suddenly stops some motion Impact spatter -Radiating pattern of small individual drops created when a blood source is broken up at a source by some force
44
what is the significance of presumptive testing in BPA?
to confirm that a substance is blood, we can't assume the identity of substances
45
define Time since deposition (TSD)
amount of time that has passed since the sample (blood) was deposited on a surface
46
what is the significance of Time since deposition (TSD), what must we know to estimate it?
-establish a timeline and context for a crime -need to know how blood degrades ex-vivo, and at what rate
47
what is the main goal of time since deposition (tsd)?
Develop a reference timeline of bloodstain degradation based on known changes to blood biomolecules over time
48
Briefly explain the degradation process of blood
changes occur in the iron molecule -blood is oxygenated and nonoxygendated -eventually, ex-vivo water will replace oxygen binding with iron -look to see how quickly the change from oxygen to water occurs
49
define Analytical chemistry and Instruments
-discipline of chemistry that uses various methods and instruments to separate, identify, and quantify matter -Instruments: tools /devices that qualitatively and/or quantitatively measure the composition, properties, structure, or state of matter
50
Spectroscopy
is the branch of science focused on the investigation of the spectra produced when materials interact with electromagnetic radiation
51
explain Visible Absorbance Spectroscopy
light source put thru prism to seperate colours, then shone thru sample (blood) then onto a digital display to provide quantitative results
52
what is the use of Visible Absorbance Spectroscopy in BPA?
-Samples with visible colour can be characterized and quantified -Depending on molecules present, changes in absorbance at specific wavelengths can give us information about sample
53
what colour are fresh bloodstains? how does it reflect on a Visible Absorbance Spectroscopy chart?
bright red chart will show high absorbancy for every colour but does not absorb orange/red
54
what colour are aged bloodstains? how does it reflect on a Visible Absorbance Spectroscopy chart?
dark brown/black chart will show absorbancy for all colours
55
explain how Visible Absorbance Spectroscopy can help to estimate the tsd of an unknown sample
if we know when degredation changes occur, we can use them to model on a graph, then we can estimate the stage of degradation of the unknown sample by comparing it to the known model
56
what are latent bloodstains?
bloodstains that cannot be seen with the naked eye
57
what is a common method for revealing latent bloodstains?
chemical reagent luminol
58
explain how luminol works
luminol + basic solution + oxidant + suitable catalyst=chemiluminescence (glow) - ferric heme (iron) group in the hemoglobin of RBCs acts as a catalyst

forensic sci (15 decks)

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