Bloodstain Pattern Analysis

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Bloodstain Pattern Analysis

• Chapter 10

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Introduction to Blood
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Did you know

• You can loose up to 40 of your blood volume and
  still survive.
• Beyond that and death is certain.

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Conditions Affecting Shape of Blood Droplet

• Size of the droplet
• Angle of impact
• Velocity at which the blood droplet left its
  origin
• Height
• Texture of the target surface
• On clean glass or plasticdroplet will have
  smooth outside edges
• On a rough surfacewill produce scalloping on the
  edges

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Passive

• Passive Bloodstains
• Patterns created from the force of gravity
• Drop, series of drops, flow patterns, blood
  pools, etc.

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Determining Distance Blood Falls

• Drops form circle when hitting surface
• Size depends on speed of blood drop

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Blood Spatter

• Determining Distance Blood Falls

• Faster drop larger diameter (size)
• Higher distance larger diameter

• Due to air resistance, speed maxes out at
  distances above about 7 feet

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Blood Spatter

• Determining Distance Blood Falls

• However, size of drop also depends on the volume
  of the drop.

• Volume depends on object blood originated from
  (needle small bat large)

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Blood Spatter
Since the volume of blood in a drop is unknown
The distance a drop has fallen cannot be measured.
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Effect of Surface

• Smooth surface smooth sphere
• Rough/porous surface may cause some splatter

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Transfer or Contact BloodstainsTransfer or
Contact

• The pattern created when a wet, bloody object
  comes in contact with a target surface may be
  used to identify an object or body part.

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Projected bloodstains

• Patterns that occur when a force is applied to
  the source of the blood
• Low, medium, or high impact spatters, cast-off,
  arterial spurting, expiratory blood blown out of
  the nose, mouth, or wound.
• Narrow end of a blood drop will point in the
  direction of travel.

Images from http//www.bloodspatter.com/BPATutoria
l.htm
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Determining Direction
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• By utilizing trigonometric functions its possible
  to determine the impact angle for any given blood
  droplet.
• SIN 0 width (a)
• length (c)

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SIN lt Width (a) 1.5cm Length
(c) 3.0cm Width (a) 1.5cm SIN lt Length (c)
3.0cm 0.5 SIN lt lt 30 degrees
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Impact

• The more acute the angle of impact, the more
  elongated the stain.
• 90 degree angles are perfectly round drops with
  80 degree angles taking on a more elliptical
  shape.
• At about 30 degrees the stain will begin to
  produce a tail.
• The more acute the angle, the easier it is to
  determine the direction of travel.

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Blood Spatter

• Determining Direction of Blood

• If more than one drop (from spatter) results, the
  point of origin can be determined

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Blood Spatter

• Determining Direction of Blood

• If more than one drop (from spatter) results, the
  point of origin can be determined

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Blood Spatter

• For each blood drop, a string can be guided back
  to the point of origin.

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Blood Evidence

• Class evidence for blood would include blood
  type. If you can determine the DNA you would
  have individual evidence.
• Blood stain patterns are considered
  circumstantial evidence in a court room. Experts
  could argue many points including direction of
  travel, height of the perpetrator, position of
  the victim, left/right hand, whether the body was
  moved, etc.

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http//www.nfstc.org/links/animations/images/blood
20spatters.swf