Blood Spatter Flashcards

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1
Q

Blood Stain Pattern Analysis (BSPA)

A

Examination of the shapes, locations, and distribution patterns of bloodstains to provide an interpretation of the events which gave rise to their origin

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2
Q

Information obtained from BSPA (4)

A

Position of a victim
Evidence of a struggle
People/objects in the room (voids)
Confirm of refute statements about the actions of the crime scene

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3
Q

Why does blood tend to contract?

A

It has an “elastic-like” property caused by the forces of attraction between the molecules of the liquid (cohesion) - tends to resist penetration and separation, causing a perfect sphere

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4
Q

Maximum speed of blood and why

A

25 feet/second due to air resistance

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5
Q

Blood Patterns (6)

A

(PASS TP)

  1. Passive fall
  2. Arterial spurts or gushes
  3. Splashes/spatter
  4. Smears/transfers
  5. Trails
  6. Pools
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6
Q

Passive fall

A

Blood falling directly to the floor at 90 degrees will produce circular drops

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7
Q

What causes more satellites?

A

Textured surface

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8
Q

Arterial spurts or gushes

A

Typically found on walls or ceilings caused by pumping action of the heart

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9
Q

Splashes/spatter

A

Shaped like exclamation points, shape and position can help locate the position of the victim at the time of the attack

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10
Q

Smears/transfers

A

Left by the bleeding victim or other at the scene depositing blood as they touch or brush against a surface

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11
Q

Trails

A

Can be left by a bleeding victim depositing blood as they move from one location to another

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12
Q

Pools

A

Form around a victim that is bleeding heavily and remains in one place

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13
Q

Spines

A

Attached to the main droplet

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14
Q

Satellites

A

Not attached to the main droplet

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15
Q

Narrow/pointed end of a blood drop points…

A

in the direction of travel

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16
Q

Point of Convergence (POC)

A

Two dimensional position determining the origin of two or more drops of blood

17
Q

Point of Hemorrhage (POH)/Point of Origin

A

Three dimensional position of where the blood originated

18
Q

Steps of finding Point of Origin (3)

A

Find the POC
Find the angle of impact (AOI)
Find the POH

19
Q

Angle of Impact (AOI)

A

Angle at which the blood hits the surface and determines the shape of the spatter drop – determines the length of the drop

20
Q

AOI Equation

A
sinAOI = width/length
AOI = inverse sin (width/length)
21
Q

POH equation definitions: x and d

A
x = the POH, the hight above POC (opposite)
d = length from center of blood drop to POC (adjacent)
22
Q

POH Equation

A
tanAOI = x/d
x = tanAOI (x) d
23
Q

Why is the POH overestimated?

A

Blood falls in an arch due to air resistance and gravity

24
Q

Low Velocity Drops (speed, size, how)

A

5 feet/second
Larger stains, 4mm and greater
Dripping blood, off knife, arms swinging, hit with rock

25
Q

Medium Velocity Drops (speed, size, how)

A

25 feet/second
1-4 mm
Hit with fist, knife, bat, club - longer blunt objects

26
Q

High Velocity Drops (speed, size, how)

A

More than 100 feet/second (mist)
Smaller than 1mm
High velocity guns

27
Q

Cast-off Spatter

A

Results when an object swung in an arc flings blood onto nearby surfaces

28
Q

What cast-off spatter can tell us (4)

A

Direction of swinging object
Velocity of object
Left or right handed
Minimum number of blows

29
Q

Back Spatter

A

Arises from the entrance wound and moves towards the weapon; most common with high velocity shot guns; can leave blood on the gun or shooter

30
Q

Higher velocity leads to _____ back spatter

A

more

31
Q

Skeletonization

A

Occurs when the edges of a stain dry to the surface; typically occurs within 50 seconds