TRAJECTORY: Definition

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Crime Scene Processing Series TRAJECTORY
ANALYSIS New Mexico State Police Criminal
Investigations Section Crime Scene Team
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Analysis

• Any type of analysis that we do is based on the
  scientific method.
• The scientific method is a defined process used
  to resolve complex problems.

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Scientific Method
Reach a conclusion.
Define the problem or question.
Collect information/data to resolve the problem.
Test the hypothesis.
Organize the information.
Posit a hypothesis.
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Analysis and Crime Scene Reconstruction

• In working to establish what happened, we are
  attempting to describe a series of events
  however, many times we will not be able to
  determine everything that happened within that
  series.
• We can only give the best explanation of the
  series of events based on the data that is
  available and we are always open to revising our
  analysis when presented with new data.

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Reconstruction

• In Reconstruction, we are trying to put together
  WHAT happened, not WHY it happened.
• In Crime Scene Reconstruction, we only document
  what can be proven empirically.
• based on observation and experimentation

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Trajectory Analysis

• Analysis of the path of a bullet, while in flight
• Its a snapshot in time
• It demonstrates the relationship between a
  firearm and the target

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Terminology

• Perforate - to pass all the way through
• Penetrate - to enter and stay in
• Primary impact - the first impact
• Second, third, etc. impacts impacts after the
  first

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Cautions

• Bullets travel in curved lines
• However, we approximate the bullets path with a
  straight line
• You must consider many things
• Ricochets
• Deflections
• Variations in surfaces
• Intervening Objects
• The pitch and yaw of moving vehicles
• The biomechanics of the human body

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Other Cautions

• Your knowledge of the firearm
• Ejection patterns
• Stippling patterns
• Powder ammunition loads
• Height weight of the
• Shooter(s)
• Victim(s)
• Not all people fire guns the same way
• Training experience
• Furniture vehicles can be moved

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Straight vs. Curved Trajectory
True trajectory CURVED LINE
Approximate trajectory STRAIGHT LINE
A bullets true flight path is a parabola, or
curved line. We approximate the flight path by
using a straight line.
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(3) Phases of Ballistics
External
Terminal
Internal

1. Internal Ballistics Inside the firearm
2. External Ballistics Between the firearm the
   target
3. Terminal Ballistics After the bullet strikes a
   target

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(3) Possible Shooter Position Zones
Most Probable
Impossible
Possible, but Awkward
ZONE 1 Most Probable ZONE 2 Possible, but
Awkward ZONE 3 - Impossible
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Forces Acting on a Bullet in Flight

• Inertia
• Gravity

• Friction (air resistance)
• Yaw

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Can Assist in Answering Questions

• Number of participants
• Location of participants
• Position /orientation of participants
• Number and types of firearms
• Direction of bullet paths
• Sequences of events

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Devises used to Visualize a Trajectory

• Rods/probes - short range
• Strings - medium range
• Lasers - long range

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Equipment That You Will Need

• Rods, cones and washers
• Angle finder
• Protractors
• Colored string and eyelets
• Ribbons / colored post-it notes
• Tripod

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Equipment That You Will Need

• Tape measures
• Chalk line plumb bob
• Scientific calculator
• Laser
• Ladders
• Cameras

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Information You Will Need

• Approximate location of the shooter(s)
• Approximate location of the victim(s)
• Number of shots fired the sequence
• Types of weapons calibers

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Two Points of Reference

• Projectile paths are most accurately determined
  when the projectile has passed through two or
  more solid surfaces

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Single Point of Reference

• For a single point, accuracy is dependant upon
• The nature of the material struck
• Styrofoam vs clothing
• The thickness of the material
• 4 thick foam vs ¼ thick foam

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Documenting the Trajectory

• OVERHEAD DIAGRAM
• ELEVATION DIAGRAM
• EXPLODED VIEW DIAGRAM (overhead view with walls
  folded down)

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Collecting Evidence

• AFTER CHEMICAL TESTING AND PHOTOGRAPHS
• FINGERPRINT POWDER AND TAPE LIFT DEFECT
• MIKROSIL CASTING MATERIAL 3-D

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At Least Two Points of Reference
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DOCUMENTATION OF VEHICLES

• SQUARING THE VEHICLE
• CENTER LINE OF VEHICLE
• A SECOND REFERENCE LINE PARALLEL TO AXIS OF THE
  VEHICLE - WHEEL HUBS
• VERTICAL REFERENCE

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Entrance Exit
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Side (lateral) Angle
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Upward /Downward Angle
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Angle
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Elevations
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ELEVATIONS
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POSITIONS
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POSITIONS
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POSITION OF VICTIMS
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CALIBERS
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MOVING VEHICLE
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DIAGRAM OF VEHICLE
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MUZZLE DISTANCE DETERMINATIONS

• These determinations are only approximations.
• Some variables that can affect these distances
  are
• The size of the gun
• The caliber of the gun
• The amount of powder in the cartridge
• Some people reload their cartridges
• Intermediate objects (clothing, etc.)

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CONTACT

• Blast destruction, tearing of the skin or
  clothing soot and powder particles mostly on the
  inside of the garment and/or driven into the
  wound.
• The outline of certain parts of the gun (i.e.
  barrel bushing, front sights) may leave an
  impression on the skin around the wound
• The gases from the explosion of the pistol tear
  the skin and create a ragged entrance wound.
• A stellate (star shaped) wound is often seen in
  head shots.

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STELLATE WOUND
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NEAR CONTACT (1-4 INCHES)

• Dark soot with dense deposits of unburned and
  partially burned powder particles are often seen
  around the bullet hole
• blast destruction is still possible in clothing
  and even skin in some cases
• Tattooing/stippling (unburned gun powder becoming
  imbedded under the skin) is often seen on the skin

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3-6 INCHES FROM THE TARGET

• Some medium to light gray soot, with a roughly
  circular pattern, or a distribution of powder
  particles may be seen around the bullet hole.
• Stippling is still possible, particularly with
  dense and/or poorly burning powders.

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What do you think this distance might be?
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6-24 INCHES FROM THE TARGET

• No soot is visible
• There will be a widely dispersed pattern of
  powder particles, often loosely adhering to the
  receiving surface
• A circular pattern of powder can be seen at
  closer distances, but the circular pattern may
  become poorly defined to nonexistent at greater
  distances.

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3-4 FEET OR GREATER

• No soot or circular rings of powder are present
• Bullet wiping may be present around the margin of
  the entry side of the bullet hole regardless of
  range

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CONCLUSION

• THE ADVANTAGE OF PHYSICAL EVIDENCE AT SHOOTING
  SCENES IS THAT IT CAN BE USED TO SUPPORT OR
  REFUTE VICTIM(S), SUSPECT(S) AND WITNESS(S)
  STATEMENTS